Robotics Event

[USMC1302]

A local high school is hosting a robotics competition and has gotten some sketchy info (IMO) on what the people that run the thing will be using to provide power. I do not know exactly what wiring method will be used, but from what I understand they have a 5c/#4 copper cable they want to connect to a 3 ph panel which is their distribution panel which will then feed (2), 1 ph panels via 4c/#6 cables. They eventually run some 20 A circuits for the kids to plug in computers and maybe some tools to work on their robots. Besides some other safety concerns, I wanted to be sure the ampacity of the feeders was not exceeded. Am I reading the table correctly in that for less than 100A, the 60 degree column is used, which would mean their #4 cable would need to be protected by a 70 A breaker max?
Also, that there should be no N/G bonds in any of the downstream panels?

 

[jeremy.zinkofsky]

Please provide the main breaker ampacity rating of the "Main Distribution Panel" and of the two "Subpanels".

As per NEC 310.15(B)(16) you can only use the 60 degree column for copper cables with a specific kind of insulation (UF & TW). I seriously doubt that those types of insulations will be used. Most likely you will be required to use either the 75 or 90 degree column (THHN, THWN, etc).

You are correct in that the subpanels neutral bars are not allowed to be bonded to the panel, only the main service shall be bonded according to the NEC.

 

[USMC1302]

I believe 110.14(c) or something close indicates for circuits 100A and less and small conductors, the 60 degree column has to be used regardless of actual insulation type?

 

[jeremy.zinkofsky]

Yes, as long as the circuit breaker is not marked with temperature rating. You have to size the wire to whatever the breaker has written on it. Most breakers have the temp rating written somewhere. Can you visually inspect? If not it is always better be more conservative when deciding conductor ampacity.

 

[jeremy.zinkofsky]

What are the ampacities of the equipment that you are talking about? Depending on that information, our discussion about which column to use may be irrleveant.

 

[USMC1302]

That's the rub. I don't know what their panel ratings are or much else than what has already been given. They state they have a #4 cable they want to connect to one of the building panels. Based on that, I thought they shouldn't allow more than a 70 breaker be used in the building panel.

 

[jeremy.zinkofsky]

If I may ask, what is your part in this? Will you be installing or overseeing any of the work?

 

[jeremy.zinkofsky]

If you are only consulting and/or just a concerned citizen, I would try to get that info to make sure that this installation is done in a safe matter.

 

[USMC1302]

This is a neighboring school system, I have no interest other than they asked, and we have kids that are involved in this activity as well. I've seen some pretty shady "event" wiring, so wanted to make sure they had some straight scoop for what they should be seeing installed.

 

[jeremy.zinkofsky]

From what you just said, I would be more concerned with the outlets being properly grounded than the ampacity of the cable. If there is a history of shoddy work that is.

 

[gadfly56]

From what you just said, I would be more concerned with the outlets being properly grounded than the ampacity of the cable. If there is a history of shoddy work that is.

Yeah, it doesn't sound like someone will try hooking up a 5HP motor for this event. Making sure that no one gets bit hard if something goes awry at a workbench seems more important.