Wire size answer (Oh, Charlie!)

Can someone please answer this one correctly. I am so tired of reading comments or arguments in regards to wire size and breakers on a compressor unit.

Same old story.
50 amp breaker on 30 amp wire.
Max breaker 50 amp
Min circuit ampacity 23 amps.
To me this means you can get away with 30 amps to run, or 50 amp max or the circuit may not trip before damage to the unit occurs.

Last compressor I had go bad, turned my breaker into charcoal. It would have also fried my wiring if it had been undersized due to load from the weak compressor.

I also find plenty of burnt wires in disconnects or panels, from what I suspect is due to oversize breakers.

Unless someone can show me how this is possible, I will continue to write up small wire and big breaker.

Charlie do you have an answer?

50 amp breaker with 10 gauge wire?

Yes. Based on the info that you have provided, it is OK.

The labeling of the listed device prevails. The conductor ampacity meets or exceeds the minimum required by the label and the breaker does not exceed the maximum specified by the label. It should probably be an HACR listed breaker.

That’s not an answer Chuck.
The tag says “max” breaker. Why not use a 30 amp breaker, would that be OK, or would it kick off at start up?

Sorry, I did not understand that to be the question. I reread the original post and still didn’t find that as the question.

Some labels specify a minimum breaker. Many times it is the same as the maximum breaker size. It would not be OK to install a breaker smaller than the minimum in this instance.

If the minimum size is not specified, determining the minimum gets more involved Here’s a good artice http://www.selfhelpandmore.com/home-wiring-usa/motor-design/hvac-and-refrigeration-nameplate-data-2002.php.

Your burnt wires are most likely due to loose connections not an over load due to wire size not to say wire size can do the same thing. Breakers are not designed to trip on the exact amp load that the breaker is rated for its more like a 125% of its rated amp draw for a stated time period in seconds or they would trip every time the compressor started. The max rated amp draw as stated on the unit label as per the MFG and its associated wire size as determined by the NEC is what you need to be concerned with.

BTW compressors have a internal overload that the mfg uses to protect the compressor more so than the breaker

Sean …

Pay attention to Charlie & Chuck. On HVAC equipment the data tag rules.

Minimum Circuit Ampacity of 25.4 amps means MINIMUM of 30amp wire
Maximum Overcurrent Protection or Breaker, etc of 50 amps … means 50amp MAXIMUM.

Can you go smaller … Yes. Problem … Could trip out on start-up OR not.

Problem likely lay somewhere other than the wire / breaker sizing.

In your example you could use 25 amp conductors and a 25 amp OCPD since they both meet the required minimums according to the NEC. The 50 amp OCPD is only providing ground fault and short circuit protection so it will not have any affect on the operation of the unit if used.

The manufacturer has figured this all out so just use the nameplate to determine the correct minimum conductor size and the correct maximum OCPD size.

Also remember that the standard protections for #14=15 amps, #12=20 amps, #10=30 amps etc. do not always apply.

All good info, Thanks.