Motor CB Sizing And switch?

[AmazingTrans]

Hi everybody,

I'm have a couple of questions which i am not sure in accord to CUL & NEC standard on sizing a 1.5HP motor that runs at 460V @ 2.4 FLA. It is use for an oil pump which a lot of times it starts and stops, and mostly run continuously.

1. What size should the Circuit breaker be size at? is it 115% higher, 125%, 150%?

2. What type of trip curve should my CB be? C? D?

Hope to hear from someone!

thanks

 

[Jraef]

When you are referring to "Trip Curves" you are implying that you plan to use an MCB (Miniature Circuit Breaker) as typically used in Europe. But you ask about the NEC and CUL (which don't directly relate, but that's a separate issue) and there are restrictions as to how you can use those here..

Assuming you are using the UL489 listed MCBs, the only ones that you possibly could use, then the answer would be a D curve, but that has nothing to do with UL, CUL or the NEC. Any trip curve would work per our rules, but anything other than a D curve will likely give you nuisance trips. If you were planning on using the UL1077 versions, they are not allowed here unless there is a UL489 listed breaker or fuse ahead of them, which makes them pointless in a motor controller.

Even if you find a UL489 rated version, it's often difficult to find a reasonable application for using those types of breakers. The best ones out there are rated no more than 10kAIC, many are rated 5kAIC and there are very few installations in the US where you can get away with anything that low.

So be careful, and if you are an OEM, please try to have some compassion for the installers in this part of the world who frequently have to be the ones to explain to the buyer that their new machine cannot be hooked up without a lot of expensive re-working of the controller because you chose to use the cheapest thing available and took advantage of their having no clue what that means. So please use a proper MCCB as your motor breaker, leave the MCBs for supplementary protector use.

As to size, read the NEC article 430 and then ask questions about what you didn't understand.

 

[zog]

So be careful, and if you are an OEM, please try to have some compassion for the installers in this part of the world who frequently have to be the ones to explain to the buyer that their new machine cannot be hooked up without a lot of expensive re-working of the controller because you chose to use the cheapest thing available and took advantage of their having no clue what that means. So please use a proper MCCB as your motor breaker, leave the MCBs for supplementary protector use.
.

Best....post.......ever.

 

[mbeatty]

Best....post.......ever.

Absolutely. Great response by Jraef.