Solar Photovoltaic Remote Disconnect

Good question...

I'd have thaught most relays with a mains voltage coil would have contacts rated at 600v Dc 16 A.

You want a mains voltage coil (110v in US?) so as soon as mains goes off contacts open.

I don't understand why you want a transformer???

Check Farnell Rs Digiket etc.

Del

Hmmm, had a quick look in Farnell...plenty of 110v relays, but none with that voltage /current rating on the contacts. Maybe you need a contactor... they had some suitably rated ..but I'm not familiar with contactors.

Some one here should be able to help...jump up and down and wave your arms...maybe someone else will notice you...

Del

Ha maybe this one from Farnell would do...

Thank you for responding. I believe this might be the answer.

If I am reading the PDF that you linked to (thanks!) correctly, I would need the first DC operated contactor, the frame 2, number 3tc4417-oA with a coil suffix of 120 AC V.

The second issue you address, (the Lock-Out, Tag-Out) is something I had not considered and I will have see if a locking switch device will be satisfactory.

Thanks again for your response - I do appreciate it!

The problem with DC is the arc length when you open the contacts: DC tends to hang on a bit longer than AC because the current is not crossing zero 60 (or 50) times per second. So the throw distance for the movable contacts in DC switching becomes problematic.

Could a fuse link be employed to over come this?

excellent answer, clears a few of my doubts too.

thank you

Answer #4 brought the most aspects to think about of the problem solution, but maybe not the all.

1. In USA you may see many situations where the means disconnect is located high above the ground. There are not relays or contactors - they are simple "mechanical type" DISCONNENTS with a switching handle operated by a long stick from the ground level. They must have a well visible OFF position (see National Electrical Code -NEC 2005-2008). It seems, from the first description that it must be safely disconnected while works are done on the electrical service or indoor installations. There is not mentioned nothing about batteries - we understood the system is battery-less working with direct connection to the grid.

2. DC voltage rating should be several %% higher than nominal 585 Vdc (open circuit = no load PV voltage). At least 150% so maybe disconnect should be rated 1000 Vdc. If there are no batteries, the disconnected DC current would be very low (much less than 16 Adc) so arc is not expected to be a problem.

3. Ambient air temperature of 110 F (43 C) creates even over 200 F on the roof (I worked on USA South roofs!). The disconnect means must be also waterproof (rain, hail, and maybe sometime snow). Visit industrial plants that must have these type of "constructions" installed and talk to an electrician supervisor! You're right - fire is no good for residential buildings and electric tweezing to the people. Any this kind of installation must be inspector approved but not the one who approved construction cranes in New Your City lately!

GA

^{"2. DC voltage rating should be several %% higher than nominal 585 Vdc (open circuit = no load PV voltage). At least 150% so maybe disconnect should be rated 1000 Vdc. If there are no batteries, the disconnected DC current would be very low (much less than 16 Adc) so arc is not expected to be a problem."}

I'm not sure I understand this statement, please expound on why you need a voltqage rating higher than the voltage you have.

why you need a voltqage rating higher than the voltage you have.

I do not need - a good practice and insurance need it. I do respect your Guru status but any response for this question WHY in this forum would probably required chapter(s) of technical writing and it likely will bring more questions.

Let me use my old instructor's "reverse engineering version of so called worst case scenario":

You are in California, the state that has thousands of PV panels installed. Assume you are an inspector who approved 600 Vdc means/safety disconnect and you are on the witness stand in the court in the lawsuit in the fire case with enormous losses.

How could you explain approval of 600Vdc unit which caused the fire? Or/ and harm of a person?

You know there are several examples of investigations that have led to rules, sometime called "rules of thumb or good practice" but are the results of analysis of those examples. There are also theoretical explanations (e.g. in Universities' text books). And the plaintiff's lawyers would ask you this question. You know -The insurance lawyers are the claver ones.

You have mention LOTO which was exactly right to bring in this discussion.

Any LOTO aspect in your # 4 Answer (highly respected by readers giving you now 4 good score) means in the USA ->> follow NEC. Germany is leading in Solar PV installation in EU so if somebody asks questions from this region, s/he should respect their VDE and safety rules.

By the way AC (alternating current) is crossing 100 times zero in EU electric systems and 120 times in the USA grids/services not 50 and 60 respectively stated in your response # 4.

If you like to discuss more these and some similar problems/aspects of electricity utilization I am ready - via any way you could suggest.

What is today's ambient temperature in LA? Does Pacific's wind helps? I just started my A/C set on 78 F and think to have it solar powered.

GA

Without a drawing in front of me I can't and won't comment on that circuit except to say, since the house is being powered by the inverter you are trying to disconnect at roof level, go over that carefully to ensure there is no way that relay stays energized.

I can comment as to the lock-out. A contactor, with auxiliary contacts should enable wiring in such a way that it cannot be reengaged except by manual means, i.e., re-energising the relay circuit will not close the relay except it be closed mechanically by pushing a button.

There should be such contactors out there.

j.

Thank you for the response. This is what is existing:

ROOF (585V 15.6 amp. (DC) ------DC conductors -------------------Inverter---- AC conductors------------20 amp breaker, 120/240V house panel (AC)

What I want to do is add a N/O relay or contactor at the roof (either on the roof or immediately inside the roof in the attic) that will disconnect the DC conductors from the array on the roof to the inverter in the garage when the house electrical meter is pulled.

ROOF –(N/O RELAY OR CONTACTOR) -----DC conductors -------------------Inverter----- AC conductors------------120/240V house panel (AC)

You cannot ignore NEC safety requirements! I.e. LOTO. 120/240 indicates North America location! Right?

You do not have battery storage.

Read # 4 and 12.

That is one hell of a whopping big solar array, 585 V.D.C. that will deliver nearly 16 amps.

I would not have thought you could get that much on the average roof.

I hope you are fused just inside the roof and that all that wire is in conduit.

My concern about your circuitry was as to the possibility that without a manual reset contactor A.C. from the inverter could keep the circuits feeding the inverter hot and thus keep the panel and other related circuits hot. If all you used was a straight contactor I could see power from the inverter keeping the contactor closed or re-closing it after it had been opened by pulling the meter.

To insure against that a contactor with its coil wired through auxiliary contacts so that it is held closed by the circuit through the contacts but cannot be restored once the contactor opens and opens therefore the coil circuit through the auxiliary contacts without manually pressing a reset button on the contactor should be installed, along with the fusing, near the roof.

I would be interested in the specs for what you have in that solar system. I have a friend who is planning such an installation.

j.

"To insure against that a contactor with its coil wired through auxiliary contacts so that it is held closed by the circuit through the contacts but cannot be restored once the contactor opens and opens therefore the coil circuit through the auxiliary contacts without manually pressing a reset button on the contactor should be installed, along with the fusing, near the roof."

Thank you, Jack, for responding. I have copied the above paragraph from your thread. Could you possibly re-state what you are saying? I am having trouble understanding what you mean.

Thanks -

A contactor normally has just the contacts for it's main purpose, in your case switching a rather heavy D.C. load.

You can also buy contactor that can not be reset except by manually pushing a button that mechanically engages the contactor.

Contactor can be ordered with additional auxiliary contacts, normally open or normally closed or both or can be bought as add-ons.

The wiring scheme for the contactor I have in mind would entail wiring the coil voltage through the normally open auxiliary contacts so that when the contactor is closed by pressing the button a holding circuit for the coil is established through the auxiliary contacts and will hold the contactor closed until the voltage for the holding circuit is interrupted, i.e., the meter is pulled. You do want to ensure that the holding circuit voltage is obtained from a source not supplied by the inverter under any condition.

That way, when the meter is pulled, holding circuit voltage is lost, the contactor opens interrupting the D.C. circuit from your solar panels, and also interrupts the holding circuit because the auxiliary contacts also open. The safety, or lockout feature, is entailed in that the holding circuit running through the auxiliary contacts cannot be restored save the button on the contactor is pushed thus mechanically reestablishing both the D.C. circuit and as well the holding circuit.

In essence the contactor serves as a mechanical switch in that the button on it has to be pushed mechanically engaging its contacts, both for D.C. and as well for the holding circuit. It acts as an electrical circuit interrupter when the holding voltage is removed by removing the meter thus interrupting the holding circuit.

What I was suggesting was that you buy a contactor that is reset by pushing a button that mechanically closes the contacts.

If you have trouble understanding this draw a diagram of the contactor circuits showing the contacts for the contactor coil. Those contacts are separate from the contacts carrying you D.C. circuit.

You should see what I am talking about.

j.

The problem with that scenario, although a good solution, is that it would require manual intervention at the contactor location, something that he is trying to avoid. If he could do that, he could just use a disconnect switch.

Maybe some additional insight into the application will help everyone understand.

This issue is something that is coming up a lot in the last few months. Fire marshals are now getting into the act and requiring that, when fire fighters enters a site to fight a fire, ALL power is disconnected. They don't want their personnel exposed to possible shock or electrocution from conductors inside of attics or in hidden conduits that are not disconnected when the fire fighters kill the utility power on arrival. They are accepting exposed and visible conduits going to disconnect switches on exterior walls, but there is a problem with aesthetics of that which is interfering with some people wanting to accept solar PV arrays on their houses, especially high-end homes where people are paying a lot to make it look good. A few Solar PV companies are offering arrays that integrate with the roofing material or lie flat on top, but the addition of the disconnect on the roof makes the extra expense for this feature untenable to some. Hence the desire to put an unobtrusive box immediately inside the attic space or if there is no attic space, something low profile (and paintable) on the roof next to the array; less "ugly" than a safety disconnect switch.

The LOTO issue is, as far as I know, the only major issue still unresolved right now. There are installations underway with the solution I proposed, but nobody has as of yet addressed the LOTO issue either. I had a meeting just this week on one project, the consensus is that the LOTO may not be necessary because the inverter has a disconnect on the DC side as well. I am not convinced however, because that disconnect does nothing for the conductors coming from the array combiner box to the disconnect. An analogy would be to say that the main circuit breaker in your house can be opened and protect the utility pole worker while he services the supply transformer. Try to convince the utility worker of that logic... So the real question still is, will a LOTO device on the contactor coil circuit suffice as a safety measure for the PV array service person. I think not. I think it will require an additional service disconnect at the array.

The proposed solution to the possibility that a control circuit lockout will not be acceptable which I offered this week was to include a simple rotary disconnect in the box with the contactor. It will not need to be rated for switching the DC, just carrying it since the switching will be done by the contactor. So it can be used only as a non-load break isolation switch. Still working on the details of that however.

This is it - what is behind the question -LOTO or do not LOTO or LOTO with a conflict with NEC. Thanks JRaef!

A solution with a visible from outside the building large box with a means operated/ switched on-off by a long stick only may create "bad taste". But what about so many poles with transformers on them along the streets, are they architecturally nice? Ask Europeans!

WE have these means all over commercial and industrial structures having outside electrical equipment. Also in residential A/C units.

Wow - what a "fascinating DC contactor case"!

But - Again: there is no full electrical designing that respect NEC.

Picture:

• Firefighters did not save a house
• Insurance(s) refused to pay damages
• Owner goes to the court.
• Here s/he (owner) is loosing the case again. Guess why?

Southern123,

I don't get your point. The idea behind NEC at base is that all electrical circuits capable of causing a fire be enclosed in a manner appropriate to preventing spread of trouble, e.g., short and fire.

If all of Moondog's wiring is encased in metallic tubing and junctions in metallic boxes, with appropriate circuit breakers and/or fusing, and in addition for the rooftop apparatus he had the appropriate lightning rods and grounding, which would meet the intent and purpose of the NEC, how would that be a problem?

The purpose of his post here was to insure elimination of any danger to emergency crew staff upon disconnect from the line by removal of the meter, further ensuring safety.

As to insurance problems that is easily satisfied. All he has to do is inform the insurance company of this, yet, unusual wiring arrangement and arrange for inspection by them and their approval and he has no legal problems in the remote instance, given all the aforementioned safety considerations and installation, of a fire directly traced to electrical causes.

The only thing in this "fascinating DC contactor case" that is unusual is the application of the apparatus. Outside the solar panels themselves virtually everything else discussed here is standard industrial application including contactors with a lockout feature. In industry working as a maintenance electrician I have had to manually reset many a motor contactor, the manual reset being there to prevent easy reset and burnout of a locked down motor.

So what is the big problem and why are such routine electrical apparatus considerations, albeit in an yet unusual venue, so "fascinating."

j.

The Problem is:

there is no full electrical designing that respect NEC. (#19)

I am not sure to give a full explanation without putting the drawings/schematics on the round table and point all elements that could be wrong! Or assumptions in selecting devices/apparatuses/protections are technically & "in good practice" correct (see # 12) but any response for this question WHY in this forum would probably required chapter(s) of technical writing and it likely will bring more questions.

It seems I was right -> more questions!

Let me just show another possible error :

CB 20 A on the output of the inverter .(What is its voltage 120 or 240Vac?).

In some calculations (done usually in designing teams)

Max DC power from PV panels is: PV source (It) produces 16 amperers at 585 volts DC.(Moondog 23 - his/her piece of info) so -> P max = 585V *16A = 9360 W dc

Assuming the modern inverter efficiency factor 0f 90%, its max (for selection CB) output power is = 9360 *0.9 = 8424 W (PF =1).

If the inverter's output voltage is 120V -> I out = 8424 VA/ 120 V = 70.2 A

If the inverter's output voltage is 240V -> I out = 8424 VA/ 240 V = 35.6 A

Here the question comes: So why it is 20 A? (NEC?). One of the possible answers (not from a Designing Documentation - sorry!) is = The inverter is selected too small and 20A is to protect it! So for what reason somebody spent about or over $5K for PV without ability to get its full solar energy?

Author wants:

For firefighter's safety, I wish to disconnect (Moondog 23 - the first piece of info).

Word ffirefighter suggests possibility of fire, right? But also Somebody could recon: Electricians in Fire Station? Electrocuted while doing work? Here we have no such info. Several answers correctly suggest LOTO means. Contactors are not suited to be LOTO. So discussion is mostly out of merit, but so fascinating!

My (a little bit sarcastic) question to it would be: why not a toggle switch (as a minimal LOTO device) in the control (AC coil) circuit of the DC contactor which have Main contacts of Nominal 1000 V dc)? More questions...more questions.

E.g. in an assumption:

If all of Moondog's wiring is encased in metallic tubing and junctions in metallic boxes, with appropriate circuit breakers and/or fusing, and in addition for the rooftop apparatus he had the appropriate lightning rods and grounding, which would meet the intent and purpose of the NEC, how would that be a problem? (#20). Another good question, but how you know it is done without A Full Designing Documentation?

Let me finish with the Court Scenario:

The judge would reject all above answers and pseudo circuit - line diagram as to be valid exhibits. Tnis is sure.

A lawyer representing Insurance Co would call to witness stand: contractor/whoever did the job, inspector (if one was inspecting the work) and giving them your / our questions will kill the case. You are still not sure? Home owners which are doing jobs required licences are allowed (at least in my town) to do in their owned buildings but are fully responsible, under the law, for their failures. They do not have revoked their licenses only , because they do not have them, but they cover all losses personally that usually are listed in a substantial insurance coverage. POssible a criminal case too.

Want to discuss? Read my #12

One point you missed.

I suggested that Moondog have his own insurance company experts sign off on the set-up. That is common in industrial situations where there may be questions. Why not at Moondog's.

Once the insurance company approves, and they certainly will not if it is not a safe arrangement, they accept responsibility.

As to the switching lockout. In case of a fire and a meter pull the manual rotary switch stays in place. The manual reset contactor drops out as soon as the meter is pulled. The suggested manual rotary switch, manual switch of any kind, would not and hence power could flow if in some manner coil voltage does not fail. I can see inverter loop-back possibilities from the inverter.

The inability of a magnetic contactor coil wired through appropriate auxiliary contacts to obtain pull-in voltage until manual reset is the lock-out that it seems is to me required.

As to access without having to climb into the attic?

Install the contactor in a weatherproof box under the eave with the reset pointing down. Keep a glass lineman's pole in the vicinity so it can be reset from the ground.

j.

That very well might work, Jack, thank you.

Nothing is 100% fail-safe, but a solid attempt at providing protection is better than not having any control over the energized DC conductors hidden behind the drywall from the attic to the garage in these two story homes, IMO.

Moondog,

I hope those conductors are in metal conduit?

I don't know who did that work but I do know some folks who don't know better think D.C. does not need to be treated with even more caution than A.C.

Just be sure that installation is safe.

j.

Am I wrong?

It seems we (responding writers) are entering a legal dispute.

It is obvious that anybody asking a question wants to get 100% safe solution as soon as possible. Moondog 23 concept was to fulfill fighters' request by using contactor/relay disconnecting DC circuit just at the output of PV panels with ability to remote control. This started Contactor discussion then LOTO (NEC legal aspect) entered discussion. It seems also not to be closed. Or could be closed if another solution would be considered replacing the contactor concept.

It is obvious for persons working in electrical fields/domain that only full Design Documentation with calculation/selection and drawings reviewed by inspectors/authorities could be a base for intelligent and legal discussion. In USA NEC is a bible for this discussion.

I appreciate Jack Jersawitz position that I could classify as a defending lawyer for Moondog 32 case. In the fictional (worst case scenario) trial he presents several assumptions. By the way, creating more questions and problems (e.g. lightning protection assuming that it is present for the building, PV direct -to-grid system has Insurance expert approval)). But Fictional Insurance lawyer will request Documentation because papers and motions work in courts. Here we do not have any. We must also respect opinions of expert JRaef. Some questions still are not answered, e.g. why 20 A protects an inverter - an answer could create next question, right?

Sun in June delivers Joules of Energy, PV cells want to produce electricity. Tempus fugit (Ancient Rome - Latin).

In the system I have looked at, the inverter is fully protected elsewhere; a full electrical engineering design has been implemented. This is only an issue with respect to the Fire Marshals insisting that all power be cut off in the event of a fire fighter entering a location. The Fire Marshals will accept that their crews understand that PV arrays are always generating in the daylight, their only concern stems from the issue of the conduits and / or conductors carrying that power to the inverter (actually to the combiner box, then to the converter). Hence their insistence that the power cutoff device be located immediately adjacent to the arrays, not some distance away on a wall or under an eave. As of a meeting yesterday, they will also not accept a pole operated device, because in the confusion of battling a fire, they do not want to have to look for the pole or climb a ladder to get to the cutoff device.

I see we have a misunderstanding.

The fire crew want a system where pulling the meter kills all power in the house including any originating on the roof.

The lockout relay or contactor we were talking about, its coil being energized by house current coming from the meter, would drop out when the meter is pulled. To ensure that and prevent any other path supplying current to that coil it should be wired, with appropriate protection, on the line side of the feed to your main breaker panel, just like fire alarm systems, fire pumps, etc. The reason for that is to ensure there is no holding current going from the inverter to the contactor once the meter is pulled.

That would ensure that pulling the meter drops that contactor out. The only purpose of the contactor being under the eave, and the presence of a pole has nothing to do with the fire department.

Once the meter is restored, after whatever event caused the fire department or anybody else to pull the meter, the pole is available so you can restore the circuit from the panels without having to climb into the attic or onto the roof.

Once again, given the aforesaid layout the fire department have no reason or need to concern themselves with the contactor nor the pole once, by testing (Pulling the meter) they determine the system operates as supposed to, no power anywhere in the house.

The pole is only there for your own utility to restore the circuit to the panels.

Further, you should point out to the fire folks, the need for the manual reset of the lockout and hence the pole with which they need not concern themselves, is precisely so that there is no vagrant, accidental path, reestablishing power to the house from the panels, putting them at risk.

They have no need to concern themselves with the reset, just understand that the contactor will drop out the moment they pull the meter.

If the folks you are talking to do not understand that scenario you need to get them to designate someone who does understand, perhaps an electrical inspector or government employed electrical engineer.

On the other hand just build it and then demonstrate it. I have no doubt, if built properly, it will work.

j.

Anyway WE need to have a proper Designing Project approved by a proper engineer/licenced inspector and updated after installation is done. 585 Vdc is not a car 12V to ignore it. Anybody considered shorting PV output in this situation to dramatically lower its voltage to safe level?

In the system where contactors/controllers(NEC) have invisible disconnecting main contacts an indication of On/Off must be provided. Not big deal - but remember to install signals in the place where firefighters and others can see them.

In industrial systems - the hand operated means are used, even they could be located high above ground or an operational platform. A few answers suggested this solution.

Southern123,

You have just convinced me you are nothing more than an educated provocateur.

"Anybody considered shorting PV output in this situation to dramatically lower its voltage to safe level?"

Shorting 585 Vdc at 15 amps would "dramatically" start one hell of a fire.

That is the most irresponsible proposition I have seen anybody put up on these forums.

j.

Take DC Circuit 101 and Lab experiment with PV before you start insult as the Guest!