Switchgear Question

[charlie b]

I am reviewing a Design Analysis (DA) document written by a person who doesn't seem to understand the nature of switchgear. Or perhaps it is me who is missing something.

It's for a military housing building, and the DA is calling for a 2000 amp main service switchgear with a 1500 amp MCB. I have already written a comment to the effect that this is overkill. But the DA description includes the statement that the breakers will all be molded case. Would that be, (A) perfectly normal, (B) unusual but not unheard of, or (C) absurd? I am inclined to say "C."

Whatcha think?

 

[don_resqcapt19]

Typically molded case breakers are used in switchboards, but not in switchgear.

 

[charlie b]

That's what I thought. But is it even possible to use molded case breakers in a swgr?

 

[Ohm2]

I am reviewing a Design Analysis (DA) document written by a person who doesn't seem to understand the nature of switchgear. Or perhaps it is me who is missing something.

It's for a military housing building, and the DA is calling for a 2000 amp main service switchgear with a 1500 amp MCB. I have already written a comment to the effect that this is overkill. But the DA description includes the statement that the breakers will all be molded case. Would that be, (A) perfectly normal, (B) unusual but not unheard of, or (C) absurd? I am inclined to say "C."

Whatcha think?

“C”

 

[noonan]

I am reviewing a Design Analysis (DA) document written by a person who doesn't seem to understand the nature of switchgear. Or perhaps it is me who is missing something.

It's for a military housing building, and the DA is calling for a 2000 amp main service switchgear with a 1500 amp MCB. I have already written a comment to the effect that this is overkill. But the DA description includes the statement that the breakers will all be molded case. Would that be, (A) perfectly normal, (B) unusual but not unheard of, or (C) absurd? I am inclined to say "C."

Whatcha think?

agree with C.

 

[Ohm2]

That's what I thought. But is it even possible to use molded case breakers in a swgr?

Technically possible but not appropriate. As you said they may not know much about switchgear

 

[infinity]

For 2000 amps why do they need switchgear?

 

[charlie b]

For 2000 amps why do they need switchgear?

That, and the MCB is only 1500 amps. As I said, overkill.

 

[infinity]

That, and the MCB is only 1500 amps. As I said, overkill.

I agree. We typically install switchboards for up to 4000 amp services. For whatever reason our engineers always choose fused switches over circuit breakers.

 

[Jraef]

The definition difference between switchGEAR and switchBOARDS is tied to the protective devices used inside, absolutely.

Switchgear is listed under UL1558 using POWER circuit breakers (either ICCBs or ACBs) listed under UL 1066. You cannot put UL 489 listed MCCBs in UL1558 switchgear, there are totally different standards for short circuit withstand testing. Switchgear must hold a fault for longer in order to allow a fault to hopefully be cleared at a lower level, ie at the switchboard, MCC or panelboard closest to the fault.

Switchboards are listed under under UL 891 and will use fused switches under UL 98 or MCCBs under UL 489. You CAN put UL 1066 power breakers into UL 891 switchboards if you so desire. Many manufacturers now dual list their PCBs as 1066 and 489 or have separate versions with different mounting arrangements.

Most likely your DA is unfamiliar with the fact that these are defined terms, which seems to me to be indicative of a lack of experience and possibly not being qualified for the job.

I run into this issue of mislabeling between gear and boards a lot at the field level, but I generally ignore it because the conversations are in context and I know what they mean. I also don’t want get a wedgie in the parking lot later for being a word nerd…

 

[charlie b]

Thanks all.

 

[electrofelon]

So just to continue with the topic to create a Learning moment:. When would switchgear typically be used in a <600 V application? I thought switchgear was much more of a MV thing, is that true?

 

[Jraef]

So just to continue with the topic to create a Learning moment:. When would switchgear typically be used in a <600 V application? I thought switchgear was much more of a MV thing, is that true?

Can be used in either application, although it is much more common in MV.

Switchgear adds another level of isolation in case everything goes wrong, in that the breakers are enclosed in a steel cell that limits collateral damage. That cell can also be drawn out of the gear for isolation and servicing. Unlike MCCBs, PCBs are designed to be serviced and rebuilt, so being able to easily remove and reinstall them for routine PM work is important regardless of the voltage.

 

[don_resqcapt19]

Most of the industrial plants I have worked at used swtichgear on the secondary of their medium voltage to 488 volt transformers. Most were fed from two transformers with a tie in the center.