To Tape or Not To Tape?

In 31 years of looking around instumentation on process plants of all shapes and sizes in several countries, not a single example of taped threads has occurred on glandings, housings and openings of proprietary instruments.

Is this a case of plumbing practices being applied to instrumentation due to excessive enthusiasm?

See the white area on the threads of the receptacle? Now you've seen taped electrical threads instaled by Rosemount at the customer's request. Welcome to the world of pharmacia.

Where is the equipotential bonding?

NEMA 4 enclosures are not intended to be water tight. They provide a "degree of protection". Put the fittings on the bottom of the box.

I should have mentioned this is the weired world of pharmacia. Different rules than the real world.

It's an instrument enclosure which is pre-mounted to the sensor and mounts the way the vendor (Rosemount) intends it to be installed on the piping run.

Doesn't matter - customer still questions it pointed down as about 12 are mounted that way.

The 31 years' observations include eight in primary pharmaceutical manufacturing and two in secondary.

How is intended to earth this equipment for personal protection in the event of a fault - not the cable armour, surely?

Is there anything else the forum needs to know to give a complete answer to this posting?

See response 10 to response 5 for grounding info and picture submitted above your response.

Sorry I'm short on supplying info. This is signal wiring. Seriously doubt if a fault in a 4-20ma circuit will hurt someone.

Equipotential bonding is there to operate the circuit protective device(s) in the event of a fault.

• For example, one possible fault is an inadvertent connection between mains power supply live to the instrument loop cables. How do the circuit protective device(s) clear this fault without endangering an operative that just happens to be hosing down the instrument?

1. Where is the equipotential bonding?
2. Why is the customer insisting on the threads being sealed? Surely there is no concern about fluids coming out or going in?
3. Is there a hazardous area consideration that the forum needs to know about?

Re: "Why is the customer insisting on the threads being sealed? Surely there is no concern about fluids coming out or going in?"

Nema 4 is intended to protect ("to provide a degree of protection") against water:

"NEMA 4 – Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, and hose-directed water; and that will be undamaged by the external formation of ice on the enclosure."

Presumably, Nema 4 would not have been specified if there was "no concern about fluids going in or coming out".

No wonder electrical boxes get full of water.

On the other hand, tape could disrupt the grounding scheme.

(Over to you, Hobson.)

The receptacle does not ground. A seperate conductor can be run for grounding the instrument if required. Usually the customer does not want the instrument grounded on a pharmaceutical installation, because the process skid ground and the PLC or DCS ground may not be the same and ground loops can occur.

Aaaargh! There is no issue with a clean earth for the instruments and a dirty earth for the power distribution! This is the way that control systems have been done for decades.

The purpose of sealing the threads is unclear. Why bother? What would be implications of doing it? And of not doing it? What does the customer's Engineering Standards say about it (something else the forum hasn't been told yet) and why?

The electrical engineers of the customer we have in house today for a FAT are the ones asking the question. We have 28 of the receptacles installed on transmitters we supplied for them sans the tape, and one believes the teflon tape is necessary to seal to NEMA 4 and the other has no opinion. They are waiting for someone above them to make the call.

Looking at pictures of past projects we have done, I can find these same model receptacles factory installed on the same model transmitters by Rosemount for customer supplied instruments, one project has transmitters with teflon tape for pharma giant L, and the other has transmitters without tape for pharma giant M. Who is right? I tried Turck, who makes the receptacles, and all they will say is the front portion, ahead of the threads is NEMA 4. From threads to the housing is our problem. Note they put an o-ring on these same receptacles at one time, but have dropped them in the last few years. You can't bury enough threads to hit the o-ring on a tapered thread installation. This lack of depth also eliminates the idea of using a sealing gland like T&B makes for cable glands.

You need to look better at the NEMA 4 specs. It is not complete a water tight seal. That I believe is more the problem. That the one questioning it believes it is and that is what he is trying to do with the teflon tape.

Not really - the real problem is this is pharmaceutical, and once a machine is accepted and the very long and tedious validation for the FDA is done, absolutely nothing can ever change without a very long and tedious re-validation. Even a change as small as taping a fitting on an instrument after validation, because it is leaking water, creates a need for re-validation. (wonder why you have to pay so much for medicines and drugs?) On the plus side, this creates guaranteed re-makes of equipment that might wear out, as they can replace with exact duplicates from the original source.

We were told this particular company has a whole plant shut down because they accepted some tanks and skids with minor errors and the process to re-validate the entire lot was more expensive than closing the facility. That is why they are so particular to details such as this.

We currently are FAT testing 14 tanks with a temp and pressure sensor, mixer, and some valves. The cabinets are merely junction boxes for the instrumentation to connect to a plant system via the old method of multiconductor cables. The mixer VFD is also plant mounted, so not part of the test. The test to accept these is going to take 3 weeks with 12 hour days and Saturdays included. (about 200 hours, or 14.25 hours per tank) Pharmaceuticals are that particular because of FDA.

Ok but if the they required a sealed tight then they should have spec out NEMA 6 or higher. Not NEMA 4. The sealing properties on NEMA 4 is limited. You didn't say what the raceways are they EMT or rigid pipe?

No raceways - this is a clean room tank with runs of much less than 3 meters - see picture above in my response, I believe it is 9 or 10. A Turck Eurofast receptacle with 1/2" NPT threads and an attached cable. There is also an issue with the plug on the opposite side un-used entry port to seal to NEMA 4 standards. Turck guarantees the cable and recptacle interface to be NEMA 4, but won't touch the threaded side issue.

More plumbing stuff....

Welllll - Did I mention this is for pharma use? - FDA approved goop only.

As an alternate to tape,use Dow Corning 111 instead. I have use this compound on these fittings for ease in removing them later. This is great product for industrial use. This compound is used on the main valve for industrial water softeners that comes in contact with the water supply. It is also great for lubricating o-rings. I have used this product on many types of applications that are exposed to elements for over 30 years. Owe, this is a very safe product to handle.

As I mentioned in response 15, the manufacturer sells them with the same receptacles facory installed as an option in both versions. We never have received taped ones when we order the standard option for the mini receptacle from them. I suspect the client who sends us the taped ones requested them that way and it is a non-standard issue. (I know the money they spend/project with Emerson (Rosemount), so they can get whatever they want)

This, to me, would imply if the manufacturer will sell them as NEMA 4 with un-taped receptacles, they must have tested them that way.

This is just an exercise by myself to let off steam - in the end we will do what ever the customer wants even if it is not a legitimate request.

Want to hear about cutting open every completed and installed cable to prove which drain wire for the shield goes with which twisted pair in a cable with 4 sets of twisted pairs, where the pairs are all foil wrapped and touching each other?

Pharma is a bit tougher - we can't use the anti-seize grease you mention.

Huh...

There is no real debate until you know what the mfr did when testing and listing the devices. Sounds to me as though they probably listed it without tape, most do because as I said, it's not about a pressure seal. Adding tape probably does not violate the Type 4 listing however, because it would be considered an enhancement to the procedure. Either that or they are not sweating the details by taping them on request.

I should add that personally, I sometimes tape the fittings if I know there is a possible corrosion issue because I find that teflon tape makes it easier to remove connections later. I used to do a lot of NEMA 4X stainless steel enclosured control panels for a food machinery OEM where the use was around spice dispensing. Many spices are highly corrosive,if we didn't use teflon tape it was impossible to remove conduits after 2-3 months. Our UL inspector never questioned it.

Apply the tape ONLY to the last few threads of engagement (those farthest from the lead tip of the threaded piece). 1. full mechanical/electrical engagement 2. full seal 3. looks as required 4. aids in future disassembly

Use of tape just doesn't seem right. From my limited experience in the pharmaceutical industry the point of the seal is to prevent contamination (hence special limited or no use of sealants), and tape is not allowed due to the fact that it can wear and contaminate the environment when the threaded connection is loosened and tightened repeatedly.

The use of tape seems strange, almost someones idea of providing a seal with something other than silicon sealant which is not allowed (has the customer approved this). NEMA 4 has an equivalent IP rating of IP66, does the transmitter have an IP rating of at least IP66?

If not, perhaps the use of an approved sealant would be better. I don't know what the standards say but the pharmaceutical industry site designers/engineers are generally good at telling you exactly what you can and cannot use in this case.

Teflon tape is used all the time by major pharmaceutical companies, but not always on electronic installations. We have built equipment by most of them. Try as you might, there is usually some device not made with sanitary fittings and the threads on that get teflon taped. Never pipe doped, just taped. See response #9 by myself and note the required teflon tape on the transmitter by a huge pharmaceutical company. They supplied this transmitter and had the tape installed by Rosemount's distributor.

Yes the transmitter is NEMA 4 and my argument to our customer is we have received them on past projects with Rosemount factory installed receptacles sans the tape, so this application should not require tape to meet NEMA 4. (I am looking at un-wiring and re-installing 28 receptacles if the tape is needed - oh, and then the customer would have to do all electrical tests over that involve these instruments and yes they would take the extra day or two to do just that)

An ideal solution to this would be an electrically conductive pipe thread sealant. I don't know if any of the Loc-Tite or other products do this. If so, there could be a decent specialty market.

Conductive is not necessary - as stated above, the receptacles by Turck do not connect ground through the body - ground is only by wire. Many pharmas do not want the equipment ground connected to their DCS instrumentation system.

I guess after reading all the postings on this subject... this comes down to two factors only.

1) Your customer wants it done, and...

2) The FDA will allow it.

If both factors are true, then tape the joints.

There is no electrical issue, with respect to the body of the transmitter being bonded to ground, as it is bonded through the stainless piping.

Maybe. The inspecting engineers are not sure if the tape is necessary or not. To tape now requires removing 28 receptacles and rewiring. Then retesting all electrical tests involving the 28 instruments affected. I suspect that since we are 8 days into the process and all electrical testing is done, just mechanical remains, that the taping may be over looked if we prove that Rosemount tested without taping the threads.

I've been a bit chicken to call them in fear they will recommend taping.

The most likely scenario is they will take the same position as Turck on NEMA 4 - that is our problem to assure sealing to the standard, not theirs, as the liability issue arises in a large way with a pharmaceutical installation. Lose one batch and you are out hundreds of thousands of dollars.

Final outcome - we had to pull all receptacles and put teflon tape on the threads.

The one instrument had a "live" feed in one side (not disconnectable through a plug and receptacle) through a cable gland made of nylon. No tape required on that. I thought it most interesting who made that call. It was neither of the EE's at our site, but the Documentation/Validation Engineer that made the final call for tape on metal threads but not on plastic threads.