Disconnect Size

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Alwayslearningelec

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I have a new 100A disconnect switch feeding a condenser unit. See schedule below. THye are telling me to connect to existing feeder that was feeding the demoed ACCU.

1. 100A seems too big based on schdule below, no?
2. Should I just assume a 100A feeder?
3. THis disconnect would more than likely be unfused?
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Here they are calling for 100A disconnects but #12 wiring. Does that make any sense> Is that even allowed? THe wire would burn up correct?

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Dennis Alwon said:
The disconnect can be 200 amps since the load is only 7 amps or so it would be fine.
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Guess I'm confused. Doesn't the disconnect need to do it's job if the amperage exceed it's rating? THey are calling for #12's so I'd think the wire would fry or the breaker in the panel would take care of that???

What's the purpose to put such an oversized disconnect switch?

If it's show #12's on the load side of the 100A disco could the line side but much larger? It only tells me to connect to existing?
 
MCA (minimum circuit ampacity) is 7.6 so that's what you size your wires off of. MOCP (Max over current protection) would be your max breaker/fuse size. 100 amps is over kill for sure but the rating of the disconnect is just the max circuit you could use it with if it is unfused it provides no OCP.
 
Alwayslearningelec said:
If it's show #12's on the load side of the 100A disco could the line side but much larger? It only tells me to connect to existing?
Click to expand...
Well something is wrong. Those units can only be connected to a 15 amp OCPD. Except for the size of the terminals which likely don't support #12 conductors the 100 amp disconnect is fine.
 
Alwayslearningelec said:
Guess I'm confused. Doesn't the disconnect need to do it's job if the amperage exceed it's rating? THey are calling for #12's so I'd think the wire would fry or the breaker in the panel would take care of that???

What's the purpose to put such an oversized disconnect switch?

If it's show #12's on the load side of the 100A disco could the line side but much larger? It only tells me to connect to existing?
Click to expand...

Don't confuse disconnect with overcurrent protective device . You can have a 100 amp disco and inside have a 15 amp breaker.
 
Krusscher said:
You would have to have a conversation with the engineer on that one. It would make sense if they had you run 100A wire and fuse it down at the disconnect for future use I guess?
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Well that was my previous question. It does say connect to EXISTING line side disconnect conductors. So even though the wire size from disco to motor is #12's, they would have 100A size wire on the line side of the disconnect?
 
Alwayslearningelec said:
Well that was my previous question. It does say connect to EXISTING line side disconnect conductors. So even though the wire size from disco to motor is #12's, they would have 100A size wire on the line side of the disconnect?
Click to expand...
Kinda hard to know that unless the put that info on the print. I guess it would be a good assumption that there is a 100a circuit there? In that case you have to use a fused disconnect and get some fuse reducers.
 
A disconnect is just a switch, the switch is not the protection. You could have a 2,000A switch if you want one and have more money than brains…

Non-fused switches have a problem with SCCR ratings though, most are rated for 10kA max without fuses.
 
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