Heat trace GFCI tripping

Status
Not open for further replies.
U

unionman

Member
Here at our facility we have a heat trace system installed in the rain gutters to melt ice. We recently repaired the gutters and repaired and replaced heat trace where needed. There are two separate zones in this building. Each zone has a control panel with 2 pole GFCI breakers protecting the heat trace circuits. When the job was complete, as you energized the breakers they would all trip when the fourth or fifth one was energized.This happens at both locations. Each zone has a transformer feeding the system, 480 to 240. I was asked to troubleshoot the system. While troubleshooting I noticed the transformer feeding the heat trace panel is delta-delta. The building is fed from a wye connected secondary main transformer. Would this configuration be causing the tripping problem? Some of the people here say the system worked fine in the past and some say it did not. I am thinking we do not have a solid neutral from the delta connection. It appears the neutral was derived from x-2 in the transformer. Would this not allow the GFCI to operate correctly? If you turn any circuit on by itself it will stay on and not trip, it is when you energize more than 3 or 4 they all trip. Any input would be appreciated, thanks.
 
Last edited:
Sounds like some type of wiring issue as the loads on one breaker should not cause other breakers to trip. Are they really GFCI breakers? If that is the case you may have a problem as normal heat trace leakage current may exceed the trip point of a GFCI device. The code requires GFP protection (30mA trip), not GFCI for heat trace.

After a bit of rethinking, it could be associated with the ungrounded delta system. There may be enough current caused by the capacitance to ground to cause the GFCIs to trip.
Don
 
Don the primary is wye, and I don't think the secondary 240 would be ungrounded.

Unionman, you say a delta-delta 480-240 V transformer feeds each load. Is this a single phase transformer or 3 phase? Is there be a new ground reference established on the secondary of the transformer or better yet tied into the grounding of the primary?

I have a feeling that there is some wiring error downstream of the GFP, or the tripping is due to the load.
 
I suspect the heat trace may have become damaged from the gutter repair. Disconnect the heat trace and ring it to ground better yet megger to ground you must disconnect both legs as they conduct to each other.
 
wirenut, it is a 3 phase transformer and all of the heat trace has been meggered and inspected. The problem starts when more than 3 breakers are energized.:-?
 
unionman said:
wirenut, it is a 3 phase transformer and all of the heat trace has been meggered and inspected. The problem starts when more than 3 breakers are energized.:-?
Click to expand...
Is is a 3 phase, 3 wire system.
Don
 
Sorry, what I meant to say was that given that the 480 service from the main transformer is a wye, there should not be any "ungrounded" systems in the building. And I was just making sure it was 3 phase :)

Unionman, when you energize the breakers, have you always energized them in the same order? Could be that there is something wrong with that 4th breaker that you always energize fourth in order.

When you say the neutral was derived from x2 of the transformer, this is confusing because I don't think x2 should be the neutral from any transformer unless it is an overhead bank type. Is this at the 480-240 volt transformer or at the main transformer?
 
I hope this helps; a GFI uses a toroidal transformer to sense only the current going out and the current returning. It "doesn't know" anything about grounds. If these two current values are unequal by 5 mA or more it assumes that current is going to ground and someone is being shocked, and it trips.
 
wirenut1980 said:
Sorry, what I meant to say was that given that the 480 service from the main transformer is a wye, there should not be any "ungrounded" systems in the building.
Click to expand...
How does the fact that the service is a grounded system have anything to do with any SDS within the building being an ungrounded system?
Don
 
hello wirenut, The fourth breaker is ok, you can put the fourth breaker on by itself and holds just fine. The same problem is occuring at the other heat trace panel at the other end of the building, nearly 600 feet away.
 
unionman said:
wirenut, it is a 3 phase transformer and all of the heat trace has been meggered and inspected. The problem starts when more than 3 breakers are energized.:-?
Click to expand...
Then it sounds like some of the circuits have been tied together somewhere do you have circuit tracing equipment available??
 
don_resqcapt19 said:
How does the fact that the service is a grounded system have anything to do with any SDS within the building being an ungrounded system?
Don
Click to expand...

Nothing really, I have just never seen an ungrounded 240 V system before. Does not mean they don't exist though :)

In looking in the NEC, it does not look like the OP SDS in the building meets any of the requirements for an ungrounded system in 250.21(A), 2008 NEC

250.21 Alternating-Current Systems of 50 Volts to 1000
Volts Not Required to Be Grounded.
(A) General. The following ac systems of 50 volts to 1000
volts shall be permitted to be grounded but shall not be
required to be grounded:
(1) Electrical systems used exclusively to supply industrial
electric furnaces for melting, refining, tempering, and
the like
(2) Separately derived systems used exclusively for rectifiers
that supply only adjustable-speed industrial drives
(3) Separately derived systems supplied by transformers
that have a primary voltage rating less than 1000 volts,
provided that all the following conditions are met:
a. The system is used exclusively for control circuits.
b. The conditions of maintenance and supervision
ensure that only qualified persons service the installation.
c. Continuity of control power is required.
(4) Other systems that are not required to be grounded in
accordance with the requirements of 250.20(B)
Click to expand...

which may support why I have not seen them. :-? However, this might be a new requirement, or I could be reading it wrong, or missing something. Anyways I'm getting off topic.

Unionman, do you have the capability to monitor current? Either rms or better yet, to get a look at waveforms when energizing? What's the size of the breakers and whats the load for the heat strips, and is there inrush current associated with them (I have never worked with these if you couldn't tell)?

Something could be tied together, but if you meggered, then that should have come up...
 
The GFP breakers do they trip if you remove the white jumpers off the nuetral bar?If not then check return path and assure you have a XO.If they still trip you have a promblem with what was wired in the field maybe same person same mistake.
 
If you have access to a good quality circuit tracer you could put it on one of the troublesome lines and if it is tied into annother circuit you will read tone at ALL breakers in the off position That it is tied to.
 
Status
Not open for further replies.
Top