Code: 480 V versus 575 V 1

[mpullin]

I am doing a new installation of some switchgear. Our current standard voltage at my facility is 575 V 3 Phase. The design for the motor controls is to have a breaker and not a fused disconnect. I was told that this is against code. My source said that this application is OK for 480 but not 575. Can somebody lead me in some direction of what is right or wrong?

 

[dbaird]

In the USA NFPA 70 NEC 2005: Article Section 430.109 covers motor disconnects.

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[dpc]

Where are you located?

 

[mpullin]

dpc,
I am located in Louisiana.

 

[RonShap]

You can have either a fused disconnect or breaker when dealing with 480V or 575. With both, you need to consider overload protection for the motor, as both the breaker and fuse do a good job of short circuit protection.

 

[dpc]

I agree with Ron Shap - either a fused switch or a circuit breaker can be used. I don't know of any NEC issues with using circuit breaker at 575V (600V).

Not that it matters, but are you talking about the disconnecting means at the starter or at the motor?

 

[mpullin]

dpc,
I agree with you both. This facility has a majority of fused disconnects and very few breakers for motor protection, so I think they were trying to shoot me a line of BS when they said it was against code. This place is a little old school and stuck in their ways and they just don't anything new. I am talking about the disconnects at the starter. Thanks for your input.

 

[dpc]

A lot of paper mills like to use fuses in motor starters instead of breakers. It may be a company policy rather than a code issue.

 

[mpullin]

dpc,
Yeh, I believe you are correct. Thanks.

 

[jraef]

Some off-shore (translation: dirt cheap) breakers are not UL listed at 600V for AIC ratings etc, so as such could not be used for that reason in the US and Canada, even though they may have IEC ratings that indicate 690V insulation. Fuji Electric is one that comes to mind, there may be others as well. It may be that at some point a vendor who only had that to sell was trying to even the playing field by implying it was a problem for everyone, when in actuality it only applied to his products, yet the memory lingers. I've seen things like that happen. Most (if not all) of the major brand name MCCBs in the US have no problem with that.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[iitm70]

One explaination for the use of fuses might be high short circuit current beyond the interrupting capacity of the circuit breakers. There are systems where circuit breakers for the desired interrupting capacity are not cost effective and fuses are used to protect the circuit.