circuit protection for new branch
circuit protection for new branch
(OP)
I need to modify a piece of equipment to include a circuit for an additional piece. The equipment is powered at 460VAC, 3-phase. The original equipment contains one step-down xfmr to 120VAC, and is protected by two primary and one secondary fuses. The add-on is 120VAC, nearly 10A max inrush. It is 120VAC input with a controller that powers a couple of 24VDC motors. Can someone tell me, or point me to the standard for circuit protection?





RE: circuit protection for new branch
http://literature.rockwellautomation.com/idc/group...
In it, a helpful standard is listed:
Circuit breaker protection for the primary side of the transformer can be
sized per NEC (National Electrical Code) Article 450-3(b)(2) which states:
”All transformers of 600V, nominal, or less, shall be protected by an
individual overcurrent device on the primary side . . .”
RE: circuit protection for new branch
It would be most helpful if you posted a schematic of your proposed system. Then we can give you advice if needed.
Best to you,
Goober Dave
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RE: circuit protection for new branch
Unless you are inside of a panel - then you need to follow the panel listing, maybe look at UL508A
Unless you can't (follow the panel listing) - then probably NEC 409, NFPA 79.
Personally I like tight primary and secondary protection of control transformers. Smoked (overloaded or internally failed) control transformers have a nasty habit of burning up the insides of control panels - while not manageing to open the fuses. Nearly iratating.
Some likely would think it is way overkill, but I don't mind getting out a fuse TCC, and verifying the energization is within the fuse rating - especially if I had not done one before.
This way you could consider it engineering - not design by regulation, which usually is not a good idea.
ice
Harmless flakes working together can unleash an avalanche of destruction