Hi, Donald,

Can't say a lot about the "Correctness" - all the specs are at work & inaccessible for a few days (and they may not apply where you are).

But meanwhile, can you please expand on "We are experiencing an abnormal failure rate ..." - what kind of failures? Is your kit failing? Trips tripping? What?

John

Hello John..

When I say "abnormal failure rate", let me give you an example:

Just yesterday, one customer sent back 9 dimmers the he "Claims" we all wired correctly.

We install flex conduit pig-tails with 18" leads out of a very well made aluminum enclosure with pure silicone gasket to prevent the elements in the Chicken House from entering the box.

All 9 of these dimmers were sent back as such:

All of the wires that were factory installed, were cut clean, inside of the box, and never used.

Somehow, I imagine the only way they could have hooked these up, is to have left the sealed door open, and run romex wire from the inside of the dimmer, back to the breaker box.

One dimmer I found with the 2 whites neutral wires still twisted together, another dimmer I found with the wires hooked up totally wrong..

All the rest, 7 dimmers had the factory wires cut up close to the PCB, so I couldn't tell if they were also twisting the neutral wires on those or not, and only one pcb board out of two were defective on those.

But meanwhile, can you please expand on "We are experiencing an abnormal failure rate ..." - what kind of failures? Is your kit failing? Trips tripping? What?

As far as I know, the breakers are not tripping, but I have had dozens of these dimmers come back with those white neutral wires tied together.

Donald

When you supply the units, what do you provide by way of installation instructions?

Is there any need (under normal installation & operation conditions) for the installer or user to open the door? If not, it may be worth supplying the units with "Warranty void if broken" tapes over the door seal.

If access is required for adjustment, could you mod the units to use sealed controls mounted on the door or panels, removing the need to open the door?

You have a liquid tight flex with 18 inch leads leaving a sealed enclosure.Is the fitting leaving the enclosure potted(sealed) around the wires to prevent atmosphere entering the box?If so, are they breaking this seal?Are your wires terminated on a terminal strip inside of the box or soldered directly to the boards?Are the wires labeled?Do the boards share a common neutral inside of the box, or are the circuits isolated from each other?

If they share a common neutral connection inside, then a separate neutral outside of the box is not nescessary, provided that the single neutral can carry the unbalanced load.If the loads are equal on opposite phases, the neutral current will be zero, unless there are some harmonic currents involved.At any rate,the neutral current will never equal the total of the two single phase currents in your application, so a #10 awg. 3 conductor with ground will suffice.Poultry houses are very long.How long are the supply wire runs?This could affect the wire size required due to derating factors.

The reason the installer is cutting your wires back and not using a second neutral is cost.He will have to install another box to join the wires to the field wiring if he uses your flex.I think he is probably mixing up the 10 volt control wiring with the 120 volt a/c wiring when he goes to the PC board.This of courese will cause a lot of board damage to the controller board.He may find his error when they don't work, and put them right, but by then it is too late.You need to check an installation before the units are removed.

A simple solution would be to provide another conduit box at the end of your flex conduit,with a labeled terminal strip, then the installer would not be tempted to open your sealed box.Pass the cost on to the customer.Also, as previously mentioned, a tamper seal on your box will allow detection of entry.MOV's on the input conductors will prevent transient spike damage.I also recommend a MOV of proper voltage across the 10 volt control, with a fuse in series with the MOV.If 120 volts is applied, it will blow the fuse before damage occurs.

Hope this helps.

You can make things fool proof, but not idiot proof.Those idiots are so darned determined.

I never did understand how contractors could expect one white wire to carry the load from two working wires(the red and black). Just get between the white wire and ground if you don't think it's carrying a load! Electricity will follow the path of least resistance. If the white wire available isn't capable of carrying the load, the juice could go through your circuit looking for another route, maybe through your components to the green wire.

Stress test a board by putting extra resistance on the white wire while monitoring flow on the green to ground. If there's a weak link, you need to know where it is.

When your customers are saying they are hooking the units up 'correctly' are they running a 12-3w/ground(or 10-3wg)? That's wiring for a 220 volt circuit, not two 110's. For your circuit they need to run two runs of 12-2wg or 10-2wg. Or a four wire cable, with ground. Check the codes in your area.

When your customers are saying they are hooking the units up 'correctly' are they running a 12-3w/ground(or 10-3wg)? That's wiring for a 220 volt circuit, not two 110's. For your circuit they need to run two runs of 12-2wg or 10-2wg. Or a four wire cable, with ground. Check the codes in your area.

I have NO idea, but a quick trip to east texas should open up a few things

Donald

I do not have my NFPA wiring reference here at home but I'm certain that not running a separate neutral for each circuit is wrong now. Your problem maybe a legacy issue though.

As far as your dimmer circuitry goes, I believe you are using SCR dimmers and not a variac. Well remember your dimmer control circuit times when the SCR gets turned ON by the timing of the voltage on the SCR gate voltage. The SCR remains ON until the current through the SCR crosses zero. With other possibly reactive circuits sharing your neutral current wire this current may not be crossing zero at zero volts. So if the SCR was designed to work on the hot or neutral side of the circuit, you could get some real strange problems.

Yes, we do provide instructions, however, we have only just lately discovered the wrong wiring.

Thanks guys for your input, I appreciate it.

Donald

Just a question, are your clients (with the faulty dimmers) using fluorescent or metal halide lamps? As you have mentioned that part of the failure is a strobing effect, it is quite possible that once the laps starters reach an operational voltage would produce a train of inductive kickbacks and high ignition currents destroying your device.

Do dimmers even work with fluorescent or metal halide lamps? Wouldn't dimming drive the starters nuts?

no, these are dimming mostly Incandescent, however they are also dimming CCFL and dimming CFL lamps

Donald

When dimmers share a neutral, the dimmer controls interact as the voltage drop in the shared neutral changes. The dimmer design probably requires a stable reference, the neutral to properly control the triac.

Not only does each dimmer need its own neutral, the neutral needs to be in the same conduit so that the electrical fields generated by the conductors cancel. Across a conduit (end to end) I've measured volts. Putting the neutrals in the same conduit, as the NEC requires, corrected the problem.

If the customer is ripping into the box to hook up his own country style wiring, I doubt he is using conduit. I've measured induced voltage in adjoining wires in a conduit.

Not telling the op how to run his business, but maybe instead of dimming, his customers could work out a way of switching lights off in some staggered fashion. Pain in the butt rewiring, probably not practical.

Another thing to think of is an isolated power supply in the dimmer. More complications.

The best bet is just void warranty on open boxes, lots of vendors do that.

The installers should be running a separate neutral for each breaker; sharing is not allowed.

Also, what are the dimmers controlling? I have seen dimmers inappropriately used for motors (ventilation fans). In this case the motors start up with "locked rotor" current draw, which could burn up your circuits. If the dimmers are only being used for resistive loads (lighting), and no circuit is exceeding your 30 amp stated load capability, the problem may be DUE to the single neutral. Exceeding the capacity of one wire significantly will cause voltage drop to occur. Without knowing the details of your circuit, this is hard to troubleshoot.

see 17

Hi Donald,

Which leg of the supply is the dimmer? the hot or the neutral?

What is the load? LED + resistance, LED driver, some other sort of lamp?

If they are in the neutral and you have split phases, i.e. 240V between hots legs and the loads are equal then the dimmers will do nothing if the neutral is shared as both loads will be in series over 240V. If the loads are unequal then the low power load will likely burn out when the dimmers are turned down.

When they are close to equal there might be some unpredictable results as the currents in the N leg will not relate either phase or voltage to the current in the hot leg.

Is it possible that with one leg dimmed that its triac is seeing voltage from the other leg, opposite polarity to that which it is expecting and this is causing the problem?

If on the other hand they are using two legs from the same phase then when one dimmer is off the second is carrying the neutral from both. Overload, burnout, when that happens the second dimmer takes the load until it, in turn, fries.

If the triacs are in the hot legs then it shouldn't make any difference whether the neutral is shared or not provided it is adequately dimensioned, although it probably contravenes code.

my .02€'s worth, hope it helps

Chas

Thanks my friend..

Us old Gray haired goats are still good for something...

Tell, me, what do I say to this "good ole boy" that called me the other day to say,

"All these dimmers are hooked up correctly, don't tell me we wired them wrong"

I'm going down there and take a bunch of pictures..

Thanks again guys

Donald

Stick to your guns. If he is opening the box and jump wiring, he is not "hooking them up correctly".

How about not having two dimmers in one box. If they are sold separately, there will be no questions about each needing it's own dedicated wiring run.

Hey DON!!

PLEASE let us know what you find out!! I for one am curious as heck.

Bill

I believe the proper label for those folks would be "installers" not "old electricians". Electricians know not to connect dimmers hot and they understand neutrals and what the NEC says about them. Too many handy-men and installers fancy themselves to be electricians because they can run some romex and wire a basic light or receptacle. What they don't know can hurt people and damage equipment. From an Old Electrician"

WOW.. so many responses/answers. I will detail more this evening, when I have more time, Once again, thanks so much for the input..

Donald

Hello Friends..

Just an update on this dimmer problem after my quick trip to Texas.

Indeed, I discovered many instances of the dimmers being installed with a shared neutral, and in every case, they had problems..

Actually, the gentleman that called me down there, didn't even have my brand of dimmer, he had similar style and design, but with no digital readout, just two circuits of Triac controlled manual dimmers, with the neutral wire shared..

His dimmers are less than two years old, and already he has 5 bad boards..

So, after much inquiry, I discovered that in East Texas, with their rolling hills, some Chicken House Pads are pushed as high as 10 feet up from the grade.

This cannot be good, with 10 feet of fill, while trying to drive an 8 foot ground rod, and find "Wet Earth" ???

Obviously, not all barns are like this, but many comments were made about insufficient Ground, in that area..

What does the main problem sould like to you folks?... I am Not saying that we have never had defective, or early failure with our components, but so many dimmers are failing, and now I discover others similar type dimmers failing in the same area..

Thanks in advance

Donald

capblanc,

I think that you are on to something. With a shared and floating neutral, not only does the opposite or OFF dimmer see 240v, but both see 240v when both are ON unless they are set to max brightness and they are driving identical loads. Since the dimmers use phase control to adjust the brightness, they each turn on and off during each power cycle. If one turns on slightly before the other, the lagging dimmer will see 240v until it turns on.

OMG,,]]

# 28 In reply to #27 Re: Digital Electronic Dimmer Shared Neutral? 10/30/2009 12:19 PM

capblanc, I think that you are on to something. With a shared and floating neutral, not only does the opposite or OFF dimmer see 240v, but both see 240v when both are ON unless they are set to max brightness and they are driving identical loads. Since the dimmers use phase control to adjust the brightness, they each turn on and off during each power cycle. If one turns on slightly before the other, the lagging dimmer will see 240v until it turns on.\ No wonder these dimmers are burning out at an alarming rate. Donald thanks guys! :o)