GFCI on 480 VAC Delta Heating Circuit

[pcarcich]

I am an engineer with a Fortune 500 company. Several years ago an operator in one of our plants reported a "tingle" adjusting a piece of equipment that was ungrounded & resistance heated using a 480 VAC 3 phase delta circuit. We immediately grounded the equipment & checked the NEC code. The electrical engineer in the plant checked the NEC code & found that GFCI is required for 480 VAC resistance heating applications. All of the 480 VAC resistance heat panels were replaced ASAP with new panels with GFCI plus all of the 480 VAC resistance heating equipment is now grounded. We are now buying a new piece of equipment for another project that is resistance heated with 240 VAC but the supplier does not include GFCI in the design because a "given amount of known leakage" in the spirally wound heated hoses would cause nuisance trips. My questions is: Does the NEC code require GFCI protection for this application or is proper grounding sufficient?

 

[charlie b]

Article 210.8 of the NEC requires GFCI protection for certain 120 volt applications. But there is no similar requirement for 240 volt or 480 volt circuits. So I don't know what the plant electrical engineer used as his or her source of information, when they told you that the heaters needed GFCI.

Article 424 deals with electric space heating equipment. I just read through it, and saw no mention of GFCI protection.

 

[don_resqcapt19]

If the heat is being used for pipelines or vessels, then 427.22 requires GFP protection. This is like GFCI but provides protection for the equipment, not people. The difference is the amount of ground fault current that is required to trip the circuit. For GFCIs it is ~5 mA and for GFP it is ~30mA.
Don

 

[megloff11x]

You may also have a local or state requirement, or an industry standard. I had a requirement of 5mA human level trip GFCI on equipment that employed 50A heaters buried in the machine. At the time, no one even made such a thing. You would have to dismantle the machine to reach them.

And they do nuisance trip.

However, the 30mA "machine" trip level will still allow about 95% or so of people to let go (I think 5mA lets 99% let go, and is below/at the low end of what causes your heart to go wild).

Tingling is bad, unless it's the electromassage machine at the chiropractor.

Did grounding get rid of the tingle? Was there another cause? If you have a leak, then the GFCI would trip and stay tripped. You are putting a tourniquet on without stitching up the lacerated blood vessel. If you repair the blood vessel, you don't need to cut off blood flow.

Matt

 

[pcarcich]

480 VAC Resistance Heating & GFCI or GFP

480 VAC Resistance Heating & GFCI or GFP

All responders:

The electrical engineer used a CD of the 1996 NEC code for his source of the information. He just typed in "GFCI or GFP for 480 VAC Resistance Heating" & did a search. He then printed out a page that stated "GFCI or GFP" was required for this application. Since then all resistance heating panels installed have included GFP. I say GFP because we recently researched the A-B ground fault circuit breaker that was used in all of these electrical panels. The GFP we installed will NOT trip fast enough & at a low enough level to protect all personel like a GFCI in a bathroom or on a hair dryer.

The grounding of the equipment did eliminate the "tingle" & when the the new electric heating panel with GFP was installed it tripped. The cause of the ground fault was a bad 480 VAC heater cartridge heater (breakdown of the wire insulation or ceramic insulation in the heater after several years service). The printout of the NEC code on allowed us to prevail & forced the issue to replace the bad equipment. To my knowledge, this type of failure has never happened again on this type of equipment. I agree with megloff11x that grounding is not a solution to this problem. The GFP will now detect when there is a problem & proper equipment grounding now insures that fault can be detected.

The "given amount of know leakage" is something that the OEM for the new equipment gave as a reason to NOT install GFP. The OEM stated in an e-mail,

"Normally, we do not use GFCI protection on our systems. The reason is: the hoses have spiral wound heater circuits encompassed with the RTD and ground. This puts a given amount of "Known" leakage to ground thus being picked up by a GFCI. I'm not saying that it's not possible to implement on these systems,I'm just saying there's a risk of nuisance tripping and if implemented we would want you to spec out the unit and have +/- adjustable trip range. Whenever we are asked about GFCI systems,we generally try and have the "End user" take some responsibility for that by way of their MMCC or the MDP".

At this time I don't trust the OEM.

 

[charlie b]

. . . He then printed out a page that stated "GFCI or GFP" was required for this application.

Any chance of laying your hands on that printout? I'd be curious to know what chapter/article number was being used to declare this to be "required."

 

[pcarcich]

GFCI on 480 VAC Resistance Heating

GFCI on 480 VAC Resistance Heating

Charlie B: I now travel alot so I am not in the plant where the 1996 NEC code CD is but occasionally get back there from time to time. I will be there on July 6th & will search for that CD to see if I can find that section.

 

[infinity]

I just thumbed through my old 1996 NEC and found nothing requiring GFCI or GFPE listed for the installation in the OP.

 

[dlhoule]

I just thumbed through my old 1996 NEC and found nothing requiring GFCI or GFPE listed for the installation in the OP.

I, also didn't see anything in the 96 NEC requiring it. I do think it is a good idea to install the GFP.

 

[pcarcich]

I finally got back to the plant but could not find the 1996 NEC code CD. I did however contact the electrical engineer who found the requirement in the NEC code. He does not have the original NEC code CD but e-mailed this info:

FROM THE 2005 NATIONAL ELECTRICAL CODE:
427.22 Equipment Protection (under section III which covers Resistance
Heating Elements)
Ground-fault protection of equipment shall be provided for electric heat
tracing and heating panels. This requirement shall not apply in
industrial establishments where there is alarm indication of ground
faults and the following conditions apply:
(1) Conditions of maintenance and supervision ensure that only
qualified persons service the installed systems.
(2) Continued circuit operation is necessary for safe operation of
equipment or processes.

For the new equipment we are purchasing:
a) Machine operators (unqualified electrical personnel) will be operating & coming into contact with this equipment
b) If a ground fault occurs, the process will cool down but no other hazardous condition will occur

The exceptions to the code therefore do NOT apply & GFP is required by the code.

 

[pcarcich]

Don Resqcapt19: The system in question is used to heat & store fluids so there are heated pipelines & vessels. You were right. 427.22 applies. Thanks.

 

[pcarcich]

don resqcapt19: You were right. The system in question melts & maintains heat on molten liquids so the system has heated pipelines & vessels. 427.22 for pipelines & vessels is the code that applies.