Fuse tripping at 160amps on 200amp load

[jstroming]

I was doing a show last week in a convention center in south florida, where our lighting kept losing power. The power service was provided by an outside electrical company. We kept tripping fuses at anything over 160 amps. This was PEAK power...not sustained, which was generally around 150amps. The electrical contractor kept stating that we couldnt pull anything more than 80% of the rated load. Knowing this was probably BS, I called 2 electrician friends of mine (one in entertainment, one not but licensed) who told me they were full of crap and probably put me on a 150 amp service and that overage blew it. My convention center contact was completely unhelpful (of course siding with the electrical contractor because they're "pros") and the IA decided to stay out of it (I dont really blame them for that). Side note, the voltage was pretty high (130V) at their termination box stage side. Of course the electircal contractor scoffed at this and wouldnt even address it. Don't know if this could be a factor. Also, before the event the electrical contractor tried to get me to use 2x 100amp services because a single 200amp service was "a pain in the ass" to run.

They are now fighting me for the balance, and I want to make sure I'm not completely off base here before I fight it. I have some industry people on my side but thought I would address the masses for differing opinions. I go by the principal where there's smoke there's fire....any thoughts?

 

[MNicolai]

Whose responsibility was it to pay to have power supplied and how far in advance did that entity know what you needed?

Did they communicate that need to the electrical contractor?

Did you ask what the EC considered their scope of work to be for this event?

What is your role with the event? We're you hired by an outside party for a one-off or are you an employee representing a company in this business relationship?

How many dots are there between you and the contractor for your needs being communicated to them?

 

[FatherMurphy]

Semantics note - fuses 'blow', and must be replaced. Breakers 'trip', and must be reset. Which did you have?

Some of the newer company switches are equipped with all sorts of sensing circuits designed to cause the breaker to trip if anything odd is going on, much like a really big GFCI. Depending on the settings, and the types of dimmers used, sometimes perfectly normal-behaving dimmers will trip the sensing circuits, when everything would have been just fine on a dumb breaker or a fuse. What sort of switch or disconnect was in use at this job? Just a disconnect, or something with lots of bells and whistles?

Were you on generated power, or shore power? You talk of power being supplied by an outside company - did they generate, or simply do all the cable running?

The 80% (or more often, 85%) rule of thumb is for continuous loads, like factory lights that are on 24/7. Short-term loads, peaks, and temporary uses should be able to hit full rating for relatively short bursts without trouble. Breakers that have often been fully loaded or over loaded can eventually go soft, and start tripping at lower currents.

 

[jstroming]

Whose responsibility was it to pay to have power supplied and how far in advance did that entity know what you needed?

Did they communicate that need to the electrical contractor?

Did you ask what the EC considered their scope of work to be for this event?

What is your role with the event? We're you hired by an outside party for a one-off or are you an employee representing a company in this business relationship?

How many dots are there between you and the contractor for your needs being communicated to them?

This has nothing to do with whether or not his statement was factually correct. I don't care if I booked the service 6 months in advance or the day before. And my position with the production is even more irrelevant. I hired a company to provide a service that in my opinion wasn't provided.

 

[jstroming]

Semantics note - fuses 'blow', and must be replaced. Breakers 'trip', and must be reset. Which did you have?

Some of the newer company switches are equipped with all sorts of sensing circuits designed to cause the breaker to trip if anything odd is going on, much like a really big GFCI. Depending on the settings, and the types of dimmers used, sometimes perfectly normal-behaving dimmers will trip the sensing circuits, when everything would have been just fine on a dumb breaker or a fuse. What sort of switch or disconnect was in use at this job? Just a disconnect, or something with lots of bells and whistles?

Were you on generated power, or shore power? You talk of power being supplied by an outside company - did they generate, or simply do all the cable running?

The 80% (or more often, 85%) rule of thumb is for continuous loads, like factory lights that are on 24/7. Short-term loads, peaks, and temporary uses should be able to hit full rating for relatively short bursts without trouble. Breakers that have often been fully loaded or over loaded can eventually go soft, and start tripping at lower currents.

Thanks for your response. It was a blown fuse, and the fuse was rated for 200 Amps. There was a simple breaker at the end of their feeder (2/0) before my dimmer. At the other end of their feeder (about 75ft) was another breaker they would not give us access to. I asked them to take a picture of the panel in the catwalk (on recommendation from a friend). They refused. And the convention center provided the power (no generator).

 

[MNicolai]

This has nothing to do with whether or not his statement was factually correct. I don't care if I booked the service 6 months in advance or the day before. And my position with the production is even more irrelevant. I hired a company to provide a service that in my opinion wasn't provided.

Take a breath.

Your position does matter. If somebody else is footing the bill and it's your job just to spec what's needed, that's a very different situation than if you have directly hired the EC. For example, if somebody else hired you and it was your job to spec the power but they would pay for it, I'd say let them deal with the EC because you've already done your job.

It's also relevant in your case not to pay the bill if the EC had been told specifically that you needed 200A in a single feed. If you told them 200A, we could even say that it being in a single feed was assumed.

I work at a company that specializes in construction management of sound and video system installs, in everything from corporate offices to sports arenas to concert halls. Don't think we don't see our fair share of "feisty" contractors -- we have a lot of experience in that matter. There's more to a situation than just a couple sentences some guy to says to you in the heat of the battle.

You asked for thoughts, I tried to gather more information so I could tell you what you've got going for in your case against the EC. Your choice if you don't want to answer the questions, but in my experience and in the experience of my coworkers, I know those questions are where you start before you start making phone calls to tell people you're not going to pay their invoices.

 

[jstroming]

Take a breath.

Your position does matter. If somebody else is footing the bill and it's your job just to spec what's needed, that's a very different situation than if you have directly hired the EC. For example, if somebody else hired you and it was your job to spec the power but they would pay for it, I'd say let them deal with the EC because you've already done your job.

It's also relevant in your case not to pay the bill if the EC had been told specifically that you needed 200A in a single feed. If you told them 200A, we could even say that it being in a single feed was assumed.

I work at a company that specializes in construction management of sound and video system installs, in everything from corporate offices to sports arenas to concert halls. Don't think we don't see our fair share of "feisty" contractors -- we have a lot of experience in that matter. There's more to a situation than just a couple sentences some guy to says to you in the heat of the battle.

You asked for thoughts, I tried to gather more information so I could tell you what you've got going for in your case against the EC. Your choice if you don't want to answer the questions, but in my experience and in the experience of my coworkers, I know those questions are where you start before you start making phone calls to tell people you're not going to pay their invoices.

My question solely revolves around the technical aspects of the situation, not administrative.

 

[Chris15]

Oh dear, it looks like we're seeing some various frustration coming out. A few deep breaths all round might be in order...

From my understanding, and remembering we work on different codes here, the 80% rule is all about the thermal performance of a breaker. It's saying that if you put more than 80% of full load on the breaker for more than 3 hours, then the breaker can't be guaranteed to properly dissipate that heat build up and may be prone to trip.
Effectively 80% is the designed limit of how much heat it can dissipate indefinitely.
So there should then be no long term issues with running 75% load and regularly peaking up to 80% even 85%. It SHOULD be able to handle peaks up to 100% of the rated load, but we all know the relationship between theory and practice...

I would contend that you requested a 200A service that was unable to deliver 200A and that they therefore did not deliver the contracted service.

 

[museav]

I understand wanting to focus on the technical rather than administrative aspects but your comment "They are now fighting me for the balance, and I want to make sure I'm not completely off base here before I fight it." seems to be directly addressing administrative and contractual rather than technical issues. The interpretation of the situation and the related technical details may all be dependent on contractual and administrative aspects. Did the Electrical Contractor have a direct contractual relationship with you or were they hired through an intermediary party such as the convention center? Did you have a contract stating that 200A service would be provided and what did their contract state they would provide?

Not doubting anything noted but your assertion that the breakers kept opening supports that they provided power, so that probably works in their favor unless you can provide some evidence that that power provided was not what was contracted. Is there anything other than anecdotal evidence? How did you ascertain the peak and sustained current draws and is there any related documentation? Is there a picture of the related breakers being 150A rated or something like that supporting that what was provided was inherently not a 200A service or that it was 150A service? If it were to get into a legal battle then your being able to support that what was provided was not what was to be provided may be critical if they have fairly clear evidence that they did provide something.

Maybe being Devil's Advocate here but 160A peak draw with 150A sustained draw seems to indicate a fairly continuous load and if they had provided 150A service then might one have expect the breaker have started tripping at more like 120A of sustained load rather than supporting 150A sustained and 160A peak loads as it apparently did? Supporting a 150A sustained load seems closer to a rated 160A continuous load than to a 120A continuous load and less than ideal conditions (inadequate ventilation, a breaker that has already tripped many times, a highly inductive load, etc.) may cause a 200A breaker to trip with a 150A continuous load. I would not be surprised if it comes down to the simple difference of their providing a 200A service but it not being able to actually deliver 200A and that is where what was actually requested and agreed to may be critical.

 

[Malabaristo]

The 80% derating is due to the fact that a fuse is inherently a thermal device. That number is based on a certain ambient temperature and duration for a continuous load--so it's not exactly guaranteed. If the ambient temperature where the fuse was located was higher than normal (not surprising if it's up in a catwalk), then drawing 150A continuously could certainly cause it to open up. The same would be true of thermal-magnetic circuit breakers. The only time you can reliably pull 200A continuously from a 200A service is if a 100% rated circuit breaker is used. These breakers are more expensive and less common outside the entertainment industry.

It's hard to say who's at fault here without knowing more about what exactly was negotiated ahead of time. I think that's where Mike was trying to get with his logistical/administrative questions. It sounds like you (or someone from your company) said 200A, and the EC assumed you would realize that it would only be 80% rated at best. He apparently didn't state that assumption and you (probably?) didn't state that you were expecting a 100% rated feed. It's an unpleasant situation for all involved, but it may have just been a simple miscommunication on both parts.

 

[jstroming]

It's hard to say who's at fault here without knowing more about what exactly was negotiated ahead of time. I think that's where Mike was trying to get with his logistical/administrative questions. It sounds like you (or someone from your company) said 200A, and the EC assumed you would realize that it would only be 80% rated at best. He apparently didn't state that assumption and you (probably?) didn't state that you were expecting a 100% rated feed. It's an unpleasant situation for all involved, but it may have just been a simple miscommunication on both parts.

What was negotiated was that I ordered a 200 amp 3phase power service and didn't get it HAHA. I pay for their expertise in this matter. If I wasn't going to get what I paid for, I should have been told. If I was only going to get 80% of what I ordered, I should have been told ahead of time and then I would have only paid 80% of the invoice.

I dont know the local convention center situation....as an EAC they are expected to. Otherwise I would run the feeder myself. When you are on the flip side and work for the producer you see a world in which you are forced to do things, pay outrageous premiums for service, and then see them DENY DENY DENY when they screw something up. That is exactly what happened here. These convention centers nickle and dime you for everything and then play the blame game when they screw up. No accountability, just finger pointing all around. As the client, your left in the middle when it very frequently isn't your fault.

I have consulted with several PM friends of mine here in NYC and it is pretty clear it needs to be worked out between the convention center and Electrical contractor. Thanks everyone for your help.

 

[STEVETERRY]

I was doing a show last week in a convention center in south florida, where our lighting kept losing power. The power service was provided by an outside electrical company. We kept tripping fuses at anything over 160 amps. This was PEAK power...not sustained, which was generally around 150amps. The electrical contractor kept stating that we couldnt pull anything more than 80% of the rated load. Knowing this was probably BS, I called 2 electrician friends of mine (one in entertainment, one not but licensed) who told me they were full of crap and probably put me on a 150 amp service and that overage blew it. My convention center contact was completely unhelpful (of course siding with the electrical contractor because they're "pros") and the IA decided to stay out of it (I dont really blame them for that). Side note, the voltage was pretty high (130V) at their termination box stage side. Of course the electircal contractor scoffed at this and wouldnt even address it. Don't know if this could be a factor. Also, before the event the electrical contractor tried to get me to use 2x 100amp services because a single 200amp service was "a pain in the ass" to run.

They are now fighting me for the balance, and I want to make sure I'm not completely off base here before I fight it. I have some industry people on my side but thought I would address the masses for differing opinions. I go by the principal where there's smoke there's fire....any thoughts?

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

 

[JD]

Also, before the event the electrical contractor tried to get me to use 2x 100amp services because a single 200amp service was "a pain in the ass" to run.

This line keeps sticking out at me. 200 amps "hard to run" at a convention center??
Are you sure they didn't just tie you on to a single 100 ?

I am assuming that you are talking about requesting a 200x3 and they wanted to tie you on to TWO 100x3 fuses/breakers.

If the load was "calculated" as compared to "measured" there is also the possibility that the load was way out of balance (One leg having a very disproportionate amount of load, while the other two legs were lightly loaded.)

Resistive loads, like conventional lamps, may draw slightly more then calculated at 130 volts, but only on dimmers that do not use regulation and not enough to make much difference. For example, a 1000 watt 120 volt lamp (at rated voltage) will draw 8.33 amps (14.41 ohms) If the 120 volt lamp was run over-voltage at 130 volts, it would draw 9.02 amps (1173 watts.) That would be in a perfect world where dimmers were 100% efficient. Dimmers are more like 97% efficient, so the dimmer would be putting out 126 volts with an input of 130 volts. At that over-voltage, the 120 volt rated lamp would be drawing 8.74 amps, or an excess or 0.41 amps.

 

[headcrab]

Maybe the fuse clips were loose. That can cause a fuse to blow below its rating.
Or maybe someone replaced a loose fuse clip with a conduit clamp.

Put some gaffer tape on it.

 

[JD]

Maybe the fuse clips were loose. That can cause a fuse to blow below its rating.
Or maybe someone replaced a loose fuse clip with a conduit clamp.

Put some gaffer tape on it.

You might be on to something. A 200 amp fuse is a real bear to blow under normal circumstances, but loose anything at high current = lots of heat.
Something is way out of whack here (imho.) You can get pretty far over the rating for very short durations and still not pop them, so the thought of transits over 160 amps taking them out doesn't sound right. Would have wanted to walk that feeder the night of as well, and see exactly what was inline.

 

[headcrab]

I'm going to guess you'd find copper at the ends and aluminum in the middle. Or fine-stranded wire under a standard lug.

I'm just throwing things out there.

 

[Edrick]

It would seem to me if one asked for a 200A Service, you would get a service rated at 200A and your job would be to factor in that 80% continuos rating. They gave you a 200A Service as requested. That being said you should be able to draw approximately 180A continuos. I might of missed it was it single phase or three phase? Were you pulling 150A Total, or 150A per leg? How did you calculate actual load with a amp meter?

 

[millamber]

I'm not going to pretend I understand the intricacies of triplen harmonics, but from what I read the neutral wire should have been rated for 140% over the phasing. If you have 150amps sustained, wouldn't that make effectively 210amps (140%) on the neutral?

I'm asking here, cause I genuinely don't know.

 

[headcrab]

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.

 

[STEVETERRY]

It would seem to me if one asked for a 200A Service, you would get a service rated at 200A and your job would be to factor in that 80% continuos rating. They gave you a 200A Service as requested. That being said you should be able to draw approximately 180A continuos. I might of missed it was it single phase or three phase? Were you pulling 150A Total, or 150A per leg? How did you calculate actual load with a amp meter?

A "200 amp service" is typically a three-phase 200A service, or 600A at 120V--at least in a typical theatre or exhibition center.

You would be able to draw 160A per phase, or 480A at 120V continuously from such a service.

ST