Does this seem right for an air compressor?

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electricblue

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The maximum fuse looks too small and the wire sizing doesn't account for 125%. This is for an air compressor. Hope I've attached this right. I was thinking 80amp wire and up to 150 amp breaker.
 

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electricblue said:
The maximum fuse looks too small and the wire sizing doesn't account for 125%. This is for an air compressor. Hope I've attached this right. I was thinking 80amp wire and up to 150 amp breaker.
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So where did that come from, and what does it relate to?

The reason I ask; They clearly state "as per UL 508A" in several places. So that would relate to the INTERNAL conductors used inside of a control panel assembled by a UL 508A listed shop, and although I'm not checking their claims against UL documents, it might be perfectly legit.

But then YOU are citing the NEC requirements. SEPARATE ISSUES. If you are the installing contractor, you must use the NEC, pay no attention to what they did inside of their panel, that is between them, UL and God.

As a GENERAL RULE, UL and the NEC are now supposed to me much more in synch, but not always when it comes to INTERNAL control panel wiring, if for no other reason than the fact that UL allows them to size conductors based on 90C ratings, whereas we (as installers using the NEC) are mostly restricted to the 75C column.

Now, if they (the compressor supplier) are foisting those UL guides as if they apply to FIELD wiring, then they are probably wrong and you were right to question it.
 
electricblue said:
I asked for the specs on the compressor and got this. It's from the guys supplying it.

ATLAS COPCO GA22VSD+ AIR COMPRESSOR ELECTRICAL REQUIREMENTS
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I would ignore their cable sizing recommendations then, unless they happen to come out larger than what you see fit for the NEC. All you really want is that machine total FLC from the third document so that you can size the feeder, based on whether it does or doesn't have the dryer. The fuse size they list is for HRC fuses, which means High Rupture Capacity, something that is used in IEC fuse designations more. Here it just means high AIC rated, which for us is always relative to whatever the available fault current really is in any given situation anyway. But in general, HRC fuses are usually also Time Delay (slo-blo), so I would use an RK1 or RK5 TD fuse, like an FRS or LPS Bussman or equivalent.

But if they don't say you can use a breaker, you can't, at least without violating their UL listing. Happens a lot with imported stuff. It's because it's easier to attain UL listing of their machine by using fuses, but they don't care about the consequences that forces us into when installing it.
 
Jraef said:
As a GENERAL RULE, UL and the NEC are now supposed to me much more in synch, but not always when it comes to INTERNAL control panel wiring, if for no other reason than the fact that UL allows them to size conductors based on 90C ratings, whereas we (as installers using the NEC) are mostly restricted to the 75C column.
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UL508a has two charts for ampacity these days. One for 60 deg C insulation and the other for 75 deg C insulation.

I do not recall UL508a ever had a means by which you could use 90 deg C ampacity numbers. Maybe before my time.

I think there is such a thing in a limited way for switchboards and MCCs though.

Look closely at the documents. It appears the second one is suggesting putting seperate fuses in each conductor of a paralleled conductor installation, which is not found in either UL508a or NEC.
 
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we can have up to 250% on the breaker. You think 80 is ok ? It's right next to the equipment, so I'm going to put a breaker lockout and use the breaker as a disco. Am I right on this?
 
electricblue said:
Why do I need fuses when I have a breaker? 430.52
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Very simple:
NEC section 430.52 tells you what OCPD devices and settings are allowable under the NEC. But none of that can override your duty to follow the manufacturer's instructions when installing the compressor.
The first of your three pages mentions circuit breakers, but all of the specific references to OCPD sizes use the word "fuse". That limits you to using fuses for OCPD protection, unless you can convince the inspector that the compressor manufacturer made a mistake and you know their intentions better than they do.
As was mentioned earlier, if the UL testing on which the equipment listing was based was done only with fuses, the equipment cannot be used with CBs instead, no matter how close the trip characteristics and current limiting of the CB may be.

Do you think you can convince the inspector whether the first page use of "breaker" was incorrect or the use of "fuse" on the other two pages was incorrect?
 
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