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Old 06-28-2012, 02:13 AM   #1
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Disconnect equipment switch


Along the lines of cut off switches.....we have a walk in cooler compressor rated 3 phase 15 amp. The Cut off (disconnect service switch) has (3) 20 mini fuses but it leads to and is wired to a 3 pole 15 amp breaker. The fuses are not hard wired- just the typical ones you pull out and can buy in the store. it is 208v. Must the fuses also be 15 amp or will the 15 amp breaker suffice since it will trip if overloaded? Curious of the reverse: If you had 15 amp mini fuses in the cut off and a 3 pole 20 amp breaker in the panel, would it be protected the same? I tend to think it is protected either way, but really should be the same amperage.

Also, it appears to have 10g wire over about 80 feet. Is this an overkill for 15a or typical on equipment the runs non stop even though it is 15 amp or is it because it is 3 phase or?

Thanks for any opinions/info.

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Old 06-28-2012, 07:42 AM   #2
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Disconnect equipment switch


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we have a walk in cooler compressor rated 3 phase 15 amp.
....wired to a 3 pole 15 amp breaker.
The Cut off (disconnect service switch) has (3) 20 mini fuses...
What amperage does the equipment actually draw?

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Old 06-28-2012, 11:40 AM   #3
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Disconnect equipment switch


Must the fuses also be 15 amp or will the 15 amp breaker suffice since it will trip if overloaded? The lower amperage circuit protection will govern when the circuit is tripped.

Curious of the reverse: If you had 15 amp mini fuses in the cut off and a 3 pole 20 amp breaker in the panel, would it be protected the same? The circuit would be protected for 15 amps.

Also, it appears to have 10g wire over about 80 feet. Is this an overkill for 15a or typical on equipment the runs non stop even though it is 15 amp or is it because it is 3 phase or? #10 wire for a 15 amp circuit with a wire length of 80 feet is overkill but doesn't create any problems. The larger wire will create less resistance and therefore less voltage drop but it is negligible. Running continuously or being 3 phase has no bearing on the wire size.
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Old 06-28-2012, 11:56 AM   #4
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Disconnect equipment switch


The 20 amp fuses are in the disconnect and are not needed at all. A simple non-fused disco could have been used. Or its possible the switch was not required. So, having 100 amp fuses (as an example) in the switch would be of no concern as the circuit is protected at 15 amps. Like Julie said above.
You have no issues as far as I can see. You might want to put a note on the switch as to where the circuit originates and what the actual circuit OL current is.
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Old 06-30-2012, 02:18 AM   #5
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Disconnect equipment switch


Thanks for confirming what I thought. I think it draws 10.4 amps but will have to recheck.
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Old 06-30-2012, 08:02 AM   #6
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Thanks for confirming what I thought. I think it draws 10.4 amps but will have to recheck.
Is this an older installation?
If so... the equipment that used to be there may have needed the heavier wire and the heavier fuses and when replaced with what you have now they just reused what was there plus the new breaker.

hth
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Old 06-30-2012, 08:08 AM   #7
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Disconnect equipment switch


Some refrigeration equipment requires fuses for the ocpd, and this may be the case.
Check the name plate for the size of circuit, and type of ocpd.
If it makes you feel better, change the fuse to 15 amp, unless the data plate tells you differently
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Old 06-30-2012, 01:52 PM   #8
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Disconnect equipment switch


Yes, I thought too that it might have either 1) been wired for a former compressor that needed the heavier wire and amps or 2) they planned for the possibility of replacement compressor possibly needing it down the road. The name plate says to protect it with 15 amp max.

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