We just had a OSHA-type consultant here. She spotted a 208v 3 phase pigtail connected to a circuit breaker box. The pigtail had a 30 amp labeled receptacle attached and the receptacle was protected by a 30a breaker on each leg. She is claiming that because the receptacle was protected by 3 30a breakers, the plug had to be rated (and marked) 90a.

It is my understanding that the 30a rated receptacle means that each of the three legs is rated at 30a and that each leg protected with a 30a breaker is correct. My opinion is seemingly unimportant as management feels that the OSHA consultant is the fount of all knowledge thus is correct.

I have two questions. (1) Am I correct or is she. (2) Where could I find printed support for my position thru NEMA, National code or anything else.

 

You are correct, the "OSHA consultant" is ignorant. There is no printed support in the code, this is considered to be basic knowledge. Each CIRCUIT must be protected against carrying too much load. A 30A circuit means nothing more than that, it can carry 30A. If you protect it with a 30A circuit breaker or fuse, the device clears (opens) the circuit if more than 30A goes through it. If you put a 90A circuit breaker on there, it will not trip until 90A is going though any one pole, which will be 3X the rating of the device. That will likely start a fire!

Some safety consultant...

 

I asked all the electrical engineers here and we all came up with the same answer ...

Your "consultant" is incorrect. The power outlet should be labelled 30A

There is a very good explanation of 3-Phase power that your consultant should perhaps refer to here -> http://en.wikipedia.org/wiki/Three-phase_electric_power

If everything is working correctly then the total current drawn from the supply should be close to zero as each phase will cancel out the others - assuming you are using all 3 phases. If your equipment is only using 1 phase, then 30A is the max that can be pulled from each individual phase.

If you were to label the power outlet as 90A and somebody were to attempt to draw 90A per phase from it, then your circuit breakers would (hopefully) trip.

There is nothing wrong with using a plug or outlet socket rated up to 90A, but it would be wrong to label the outlet as being able to supply 90A - it cannot.

I assume that your consultant is not telling you to change the 30A circuit breakers to 90A. They are in fact instructing you to label the power outlet incorrectly.

Rob