Fuse tripping at 160amps on 200amp load

[STEVETERRY]

That won't blow a fuse unless there's one in the neutral for some reason. Harmonics only cause trouble for wire size and the supplying transformer.

There shouldn't be, but how do we know there actually wasn't? Maybe the installing electricians accidentally fused the neutral? It is said that something similar happened: a scrap of white tape caught on a wire that was being pulled in. This was, I believe, a service, so many large wires that are legal to re-code as white. Someone saw the white scrap, assumed it was supposed to be a neutral, and recoded said wire as a neutral. Someone (may or may not have been the same person) landed said wire on a phase lug...

I expect that made a bit of noise.

The NEC does not allow an overcurrent protective device in the neutral on a wye service. Typical three-phase wye switchgear would have no provision for a fuse in the neutral.

And actually, harmonics are a prime cause of overcurrent protective devices tripping or clearing "apparently" at current levels well below their rating.

However, "If you hear hoofbeats, don't suspect zebras."

There are many other plausible explanations to this situation--I hope to get to some of them if the OP answers my earlier questions.

ST

 

[Goph704]

Steve
I can't tell but I think he may be done with this thread. Just for my education.......... Assuming Thermal breakers, sustained load of 150 amps, a peak load of 160 amps and A de-rated service, In one of your scenario's could the Florida Temperature possibly be the culprit? Would the thermal breakers be more likely to trip under those conditions? I remember going crazy trying to keep dimmers cool when I was working in Orlando, and earlier in the thread he mentions that the service was up in the Catwalk. It would get pretty hot up there I would imagine. But I'm still confused as to why the contractors would try an bring in a service that the knew was a "pain in the ass."

 

[jstroming]

Some questions to help us help you:

1. Was the load calculated or measured?
2. If it was measured, what instrument was used?
3. What types of loads were connected? Dimmers and tungsten loads, arc-source loads, LED's etc?
4. Were the loads 120V, 208V, or a mixture of both?

ST

Sorry I've had a busy day.

1> Measured
2> A few different clamp-on ammeters. All were reading about the same at different points on feeder.
3> Dimmers, LEDs and movers. After PD split
4> everything 120V.

 

[STEVETERRY]

Steve
I can't tell but I think he may be done with this thread. Just for my education.......... Assuming Thermal breakers, sustained load of 150 amps, a peak load of 160 amps and A de-rated service, In one of your scenario's could the Florida Temperature possibly be the culprit? Would the thermal breakers be more likely to trip under those conditions? I remember going crazy trying to keep dimmers cool when I was working in Orlando, and earlier in the thread he mentions that the service was up in the Catwalk. It would get pretty hot up there I would imagine. But I'm still confused as to why the contractors would try an bring in a service that the knew was a "pain in the ass."

Breakers are typically calibrated at 40 degrees C ambient (104 degrees F).
If it was above that at the breaker location, that could have affected the trip current.

ST

 

[STEVETERRY]

Were the ammeters True-RMS responding, or cheap-and-cheerful types? Manufacturer and model numbers would help. Humor me--this could be part of your issue.

With 160A of load on a 200A thermal breaker, you have little or no margin for error. 80% loading = 160A.

A non-true-RMS meter could have lied to you and let you believe you were OK.

ST

 

[jstroming]

2 of us had Kluge ammeters. Don't know model numbers, but they were both True-RMS.