Conductor size

That’s what I would do.

430.22 refers to 430.6 A1. Which says to use 125% of tables in back 430.247 -430. 250 instead of nameplate.

Table 248 5HP
208 30.8A
230 28A

Motor is tripping overloads, and company supplying compressor said it needed #8.

Based on the table I can not deny.
But I would have run #10
 
As stated you need to use the NEC tables for the amp draw not the nameplate. Why is the overload tripping?
 
That is the question. I don’t think it has anything to do with the fact that #10 was installed instead of #8. Tell me I am wrong. The breaker isn’t tripping. Based on that I’d think that that the 30 amp wire and breaker would be sufficient.

Would the current installation cause motor overloads to trip?

Haven’t dealt with a lot of motors over the years other than provide appropriate power to. Never had any call backs as far as I know.
 
Measure the amp draw.
If it’s high, either there’s too much load (compressor problem, too high pressure setting…) or low voltage.
 
OK Sparky 93 said:
430.22 refers to 430.6 A1. Which says to use 125% of tables in back 430.247 -430. 250 instead of nameplate.

Table 248 5HP
208 30.8A
230 28A
Click to expand...
So is the motor supplied with 208V or 240V? For 240V, 28A * 125% = 35A, which is the 75C ampacity of #10. Meaning if it's supplied by a 75C wiring method, #10 Cu is sufficient.

Cheers, Wayne
 
Considering the numbers the OP provided and the fact that it's a compressor I would bet it's not a true 5HP.
The nameplate might well show SPL for HP.

Is this a new installation ? If not, have there been any changes (motors, pulleys, location, etc) ?
 
augie47 said:
Considering the numbers the OP provided and the fact that it's a compressor I would bet it's not a true 5HP.
The nameplate might well show SPL for HP.

Is this a new installation ? If not, have there been any changes (motors, pulleys, location, etc) ?
Click to expand...

He stated existing installation. For how long

I agree, it’s likely not a standard NEMA rated motor.
 
They say there are no such things as dumb questions.. so here goes...

If you are around this compressor, do you know if the overloads trip when starting up with the tank Empty?

Or does it trip when starting up when the tank is full, and the pressure switch just closed at the cut-in point?

Or both?

It's possible that the pressure relief valve is not venting properly (when the motor/pump cycle off) and when starting up with the tank already pressurized the piston is fighting hard to get those first few strokes in against some heavy head pressure.

If there was a compressor company looking over this problem, I have to assume that they'd find that problem out in a heartbeat.

#10 copper and 200 feet and 30 amps shows ~ 5.7% VD. Not super crazy, but you are getting down to ~196 VAC (if starting from 208). And if the motor is at all undersized, it could be struggling at startup some. Measuring start-up voltage available at the motor would be a good data point - especially if summer time voltages in your area are on the low side. Our commercial shop could typically be 202 VAC in the summer daytime.

You could get a reasonable feel for an undersized motor by watching an amp clamp meter and tracking motor current as the tank pressure heads towards the cut-out point. Comparing the max current seen against the motor nameplate might give you a clue.
 
wwhitney said:
So is the motor supplied with 208V or 240V? For 240V, 28A * 125% = 35A, which is the 75C ampacity of #10. Meaning if it's supplied by a 75C wiring method, #10 Cu is sufficient.

Cheers, Wayne
Click to expand...
My thoughts too. If it was 208V, then the minimum conductor ampacity would be 38.5A and #10 would be too small. So not knowing the actual voltage makes it difficult to assess further.

Side note: in my experience 9/10 when a compressor starts tripping the OL relay after having run fine for years, it's a stuck unloader. For some of them, the unload valve is combined with a bleeder function, so it;'s on the bottom of the tank to facilitate blowing the water accumulation out when it unloads. If that water sits in there too long, it rusts the tank and that rust clogs the unloader valve to where it stops working, and the compressor can't accelerate into a closed system.
 
augie47 said:
Considering the numbers the OP provided and the fact that it's a compressor I would bet it's not a true 5HP.
The nameplate might well show SPL for HP.

Is this a new installation ? If not, have there been any changes (motors, pulleys, location, etc) ?
Click to expand...
Good catch. The posted nameplate is very close to a standard 3HP NEMA motor.
If the installer used 5HP as the motor, referred to the motor tables, and used 30.8A as the FLA, it could result into an overload protection setting that will be above the actual motor FLA rating way too much. OL setting of 100% (30.8A) will trip at 35.4A. 35.4A is 48% higher than the nameplate current rating! The compressor could have burnt out before the protection trips.
 
topgone said:
Good catch. The posted nameplate is very close to a standard 3HP NEMA motor.
If the installer used 5HP as the motor, referred to the motor tables, and used 30.8A as the FLA, it could result into an overload protection setting that will be above the actual motor FLA rating way too much. OL setting of 100% (30.8A) will trip at 35.4A. 35.4A is 48% higher than the nameplate current rating! The compressor could have burnt out before the protection trips.
Click to expand...

These special compressor motors usually have built-in thermal OLs.
 
retirede said:
These special compressor motors usually have built-in thermal OLs.
Click to expand...
Yeah. "compressor motors", that is. The OP mentioned something like "motor for compressors". I then assumed they're not the special hermetic compressors for A/Cs or refrigerators.
 
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