Compressor disconnect- recommendations wanted

[iceman510]

I am preparing to wire in my compressor. It is a 5 hp so as I have learned here, it needs to be wired in directly and I need a disconnect (in a different room than the breaker box).

Question is, does this disconnect need to be fused? I suspect it doesn't since it is on it own breaker. I don't particularly like the pull-out disconnect type like is often used for A/C installations, but they seem the cheapest. Recommendations or suggestions for a type to use? I was thinking something like this:

http://www.menards.com/main/electrical/circuit-protection-distribution/safety-switches-disconnects/ge-30-amp-indoor-non-fused-safety-switch/p-2289756-c-6435.htm

Fusible type is much cheaper.

Thanks for any input.

 

[pattenp]

I suggest this one. It's just a switch, not a breaker.

http://www.menards.com/main/electri...sed-ac-disconnect-switch/p-1736468-c-6435.htm

 

[freshintulsa]

I just wired up my 7.5 hp compressor and used the square d one in the link that pattenp posted. works great and its cheap!

 

[iceman510]

I suggest this one. It's just a switch, not a breaker.

http://www.menards.com/main/electri...sed-ac-disconnect-switch/p-1736468-c-6435.htm

That looks great. Must have missed that one. Now, I am planning a 30 A breaker in the box since the motor is only rated at 15A. The 60 for this won't matter because it is not a breaker, correct? That is just the rated capacity?

 

[7thDimension]

...The 60 for this won't matter because it is not a breaker, correct? That is just the rated capacity?

Yep, that's right.

 

[wyliesdiesels]

That looks great. Must have missed that one. Now, I am planning a 30 A breaker in the box since the motor is only rated at 15A. The 60 for this won't matter because it is not a breaker, correct? That is just the rated capacity?

U said your compressor is 5HP? A 5HP motor should have an FLC close to 28a. If your comp lists 15a then the HP rating is bloated...If your compressor is truly rated at 5HP, thrn a 30a breaker may suffer from nuissance tripping due to in-rush currents...

 

[iceman510]

Perhaps a bit of bloating...

In the previous house I had no nuisance tripping on a separate box in the garage with a 30A breaker and it plugged into a wall socket with a cord. Not sure if that was ok then, but did that back in 1999, and if wrong I didn't know any better.

Now I expect it to work fine and it will be direct wired. I can still use the cord wire with the plug end removed to direct wire it, correct?

Is FLC "full load current"?

 

[Norcal]

Perhaps a bit of bloating...

In the previous house I had no nuisance tripping on a separate box in the garage with a 30A breaker and it plugged into a wall socket with a cord. Not sure if that was ok then, but did that back in 1999, and if wrong I didn't know any better.

Now I expect it to work fine and it will be direct wired. I can still use the cord wire with the plug end removed to direct wire it, correct?
Is FLC "full load current"?

Nope, use sealtite or metal flex, (Greenfield), a cord is not supposed to be a substitute for permanent wiring.

 

[wyliesdiesels]

Yes FLC is full load current. But u are to size the wire based on the NEC FLC chart NOT the FLA on the motor!

 

[iceman510]

So if I am understanding that correctly (and table 430.248 that I found), the FLC of 28 means I should use at least 10 AWG correct? I have some of that wire and found an appropriate length of BX (which I believe is what is referred to by the name Greenfield above). With the disconnect mentioned above, I should be good to go.

Sick of using my 4 gallon pancake that can't power anything but nailers.

Thanks all.

 

[Norcal]

BX is slang for armored cable, greenfield is slang for flexible metallic conduit, BTW the stuff they sell in the big box stores is metal clad, not armored cable. AC, & MC cables are solid wire which is not a good thing when vibration is present.

 

[pattenp]

So if I am understanding that correctly (and table 430.248 that I found), the FLC of 28 means I should use at least 10 AWG correct? I have some of that wire and found an appropriate length of BX (which I believe is what is referred to by the name Greenfield above). With the disconnect mentioned above, I should be good to go.

Sick of using my 4 gallon pancake that can't power anything but nailers.

Thanks all.

Yes and no. 28A X 1.25 = 35A. So #10 Romex is a no, max is 30A. If THHN then yes, max is 35A for #10 THHN.

 

[theoldwizard1]

Look at A/C disconnects, fused or un-fused. Under $20.

 

[wyliesdiesels]

BX is slang for armored cable, greenfield is slang for flexible metallic conduit, BTW the stuff they sell in the big box stores is metal clad, not armored cable. AC, & MC cables are solid wire which is not a good thing when vibration is present.

And BX is no longer made. It has conductors with rubber insulation...Been replaced with AC...

 

[theoldwizard1]

And BX is no longer made. It has conductors with rubber insulation...Been replaced with AC...

I like "seal tight", liquid proof, flexible conduit. A bit pricey so you need to find a place that will cut to length.

 

[iceman510]

Yes and no. 28A X 1.25 = 35A.

What is the basis for this multiplier calculation? In other words, what is it taking into account or compensating for?

 

[pattenp]

What is the basis for this multiplier calculation? In other words, what is it taking into account or compensating for?

It's a NEC requirement that conductors are to be sized at 125% of the motor full load current rating. The 125% is also a requirement for any circuit supplying continuous loads. It's a safety margin so not to overload circuits.

 

[iceman510]

Understand. Thank you.

I have THHN for the connection from switch to compressor. I will have to check the size/type of the wiring from subpanel to switch.