3/4" liquid tight conduit

[PT Doc]

I would like to run 3/4" liquigtight conduit when hardwiring my compressor. It is a Quincy 5 hp 80g. I would like to get 4 strands of 8g wire from the wall to my on and off switch. 1 extra MIGHT be for a 120v fan at a later time. Don't think 8g x4 would be ok in 1/2 LT conduit. Only issue is that the pressure switch on the comp has 1/2 opening.

Do the 3/4" LT fittings come in 1/2 trade size? I would need a 90 degree at the pressure switch. Metal or plastic would do.

Thanks for the help.

 

[manwithtools]

Nope, 3/4" is 3/4". I struggle to understand why the pressure switches on these compressors utilize such small openings and terminations. If you look at the pressure switch you will be hard pressed to get anything larger than 10 ga terminated in those terminals.

 

[BreeStephany]

3/4" LFNC-B can hold 6 #8 conductors, 1/2" can only hold 3, so you will have to use 3/4" throughout, including fittings, in order to be to code. Are you pulling a grounding conductor with your conductors?

You can use a step bit or 3/4" greenlee punch to enlarge the hole on the pressure switch to a 3/4" trade size hole.

 

[walrus]

I would like to run 3/4" liquigtight conduit when hardwiring my compressor. It is a Quincy 5 hp 80g. I would like to get 4 strands of 8g wire from the wall to my on and off switch. 1 extra MIGHT be for a 120v fan at a later time. Don't think 8g x4 would be ok in 1/2 LT conduit. Only issue is that the pressure switch on the comp has 1/2 opening.

Do the 3/4" LT fittings come in 1/2 trade size? I would need a 90 degree at the pressure switch. Metal or plastic would do.

Thanks for the help.

Make the 7/8 hole, a 1.125 inch hole and use 3/4. Unibit or KO punch

 

[Norcal]

Make the 7/8 hole, a 1.125 inch hole and use 3/4. Unibit or KO punch

A 7/8" hole is for 1/2" trade size fittings, also do not think the pressure switch will accommodate 8 AWG.

 

[walrus]

A 7/8" hole is for 1/2" trade size fittings, also do not think the pressure switch will accommodate 8 AWG.

That's why I said make it a inch and 1/8 hole.

 

[Aceman]

If you are running conduit, use Thhn. You do not need #8 for a 5hp when using thhn, #10 is fine.

Second, you don't want to open the pressure switch hole up to fit 3/4" conduit. Most pressure switches have covers designed to fit over the top of them and the 1/2" conduit that feeds them.

Basically, if you're trying to run 3/4" into a pressure switch, you're doing it wrong.

Third, you should be using a pressure switch to activate a starter rather than trying to start the motor directly. Generally, there are only two small control wires to the pressure switch, that in turn, activate the starter coil.

 

[sberry]

I agree with these guys, use 1/2 and 3 strands of 10 and skip the might need some **** later. If you want a fan hook it up from another circuit independent of this and keep is simple.

 

[wyliesdiesels]

I would like to run 3/4" liquigtight conduit when hardwiring my compressor. It is a Quincy 5 hp 80g. I would like to get 4 strands of 8g wire from the wall to my on and off switch. 1 extra MIGHT be for a 120v fan at a later time. Don't think 8g x4 would be ok in 1/2 LT conduit. Only issue is that the pressure switch on the comp has 1/2 opening.

Do the 3/4" LT fittings come in 1/2 trade size? I would need a 90 degree at the pressure switch. Metal or plastic would do.

Thanks for the help.

Why are u running 4 #8s?

The EGC/grounding conductor can be smaller and #10 THHN is whats needed for a 5HP motor.

 

[manwithtools]

There's not room to terminate anything larger than 10 ga. There is not room to open the conduit opening to anything larger than 1/2". You are stuck with that. You folks have not seen a recent 5hp compressor pressure switch have you?

 

[manwithtools]

If you are running conduit, use Thhn. You do not need #8 for a 5hp when using thhn, #10 is fine.

Second, you don't want to open the pressure switch hole up to fit 3/4" conduit. Most pressure switches have covers designed to fit over the top of them and the 1/2" conduit that feeds them.

Basically, if you're trying to run 3/4" into a pressure switch, you're doing it wrong.

Third, you should be using a pressure switch to activate a starter rather than trying to start the motor directly. Generally, there are only two small control wires to the pressure switch, that in turn, activate the starter coil.

Which 240 volt 5hp Quincy compressor are you describing that has two control wires going to a starter? It's just not that way in a consumer single phase air compressor, it's a pressure switch that the manufacturer says is rated to start a 5hp motor - that's all you get.

 

[PT Doc]

1/2" LT with 1/2" fittings and 10 wire qty 4 will sort me out real nice. Thanks

 

[sberry]

Whas the 4th wire for?

 

[Junkman]

Which 240 volt 5hp Quincy compressor are you describing that has two control wires going to a starter? It's just not that way in a consumer single phase air compressor, it's a pressure switch that the manufacturer says is rated to start a 5hp motor - that's all you get.

Then your 5 horse power motor is a consumer grade motor, and as such, it isn't the same as a commercial grade 5 HP motor. Please post a picture of the data plate of the motor.

 

[manwithtools]

Look at page 12 of this manual - I'm pretty sure this is the pressure switch the OP has on his Quincy. It's what came on my 5hp Quincy bought late last year.

http://www.aircompressorsdirect.com/manuals/quincyqtmanual_2.pdf

I'm not saying it shouldn't have a motor starter, I'm saying as factory assembled equipment, it does not have one. The accompanying manual shows the recommended wiring connection.

I'm not where I can get a picture of the name plate on my compressor just now.

 

[manwithtools]

Then your 5 horse power motor is a consumer grade motor, and as such, it isn't the same as a commercial grade 5 HP motor. Please post a picture of the data plate of the motor.

I'm curious what your criteria is to determine consumer vs. commercial? In my world it's more about efficiency.

If you are looking at the NEC Table 430.248 for 5 hp 230 volts it indicates 28 amps. Interesting that they do this, because at this amperage (28) and voltage (230) you would expect to obtain 7.77 HP. Total watts / 746 * efficiency. This represents a theoretical motor with an efficiency below anything commercially available today - somewhere around 64%.

If you look up Baldor's (one of the more respected motor manufacturer's) offerings for this motor, most are around 20.8 to 22 amps. Interesting again because that equals 5.19 HP to 5.49 HP if you use the formula of HP = watts / 746 * eff (.09).

The motor most Quincy 5 HP single phase compressors receive is a Baldor 230 volt, 20.8 amp 5 HP motor with 1.15 service factor and 90% efficiency resulting in ~5 hp @ 20.8, not 28.

A "commercial grade" motor has little to do with how much current it draws. There are however other factors though - bearings, insulation, winding consistency, etc.

 

[woodduder]

We need to see the nameplate to determine the motor amperage draw. When wiring a motor only load, then #12 THHN can be loaded to 25 amps and not restricted to a 20 amp breaker.

If the amperage is not over 25 you can use #12 wire and put that on a 40 amp circuit breaker without issue. This is OK since it is a motor only load.

Sent from my SM-G920V using Tapatalk

 

[manwithtools]

Wire size and circuit protection is determined by NEC HP table. Thermal overload is determined by motor name plate.