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#181549 - 10/15/08 02:57 PM Motors  
brsele  Offline
Member
Joined: Jul 2008
Posts: 89
Northern Ontario
First off, let me say that motors are my personal area of weakness.
Knowing that they are my area of weakness, I’ve tended to try to avoid them.

However, I have a small job now for an existing customer, that I think would be a good job to review motor basics as covered by the CEC.

The customer has a small shop and wants to hook up a compressor.
The compressor is 240V and the nameplate says 15A.
The compressor has a thermally protected motor and an on/ off switch.
The panel feeding power is an old one with plug fuses and is within 9m of the compressor.

Because the compressor has a switch and is thermally protected, I can just feed it with 12/2 and fuse it between 20A up to a max. of 45A.
Correct?

Now some confirmations please relating to motors.
If the compressor didn’t have a switch, then I would need a disconnect switch. A 20A DPST switch would work for this purpose. Correct?
If the compressor didn’t have a switch but the circuit was fed through a breaker panel, then would the circuit breaker count as the disconnect switch?

If the compressor motor wasn’t thermally protected, what would be the most cost effective method of providing this?

Thanks in advance. Sorry for the long post.

Bruce


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#181551 - 10/15/08 04:57 PM Re: Motors [Re: brsele]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
Originally Posted by brsele
First off, let me say that motors are my personal area of weakness.
Knowing that they are my area of weakness, I’ve tended to try to avoid them.

However, I have a small job now for an existing customer, that I think would be a good job to review motor basics as covered by the CEC.

The customer has a small shop and wants to hook up a compressor.
The compressor is 240V and the nameplate says 15A.
The compressor has a thermally protected motor and an on/ off switch.
The panel feeding power is an old one with plug fuses and is within M of the compressor.

Because the compressor has a switch and is thermally protected, I can just feed it with 12/2 and fuse it between 20A up to a max. of 45A.
Correct?
See 14-510 and 28-200 to 28-204

Now some confirmations please relating to motors.
If the compressor didn’t have a switch, then I would need a disconnect switch. A 20A DPST switch would work for this purpose. Correct?

Sorry, see 14-510 and maybe it does

If the compressor didn’t have a switch but the circuit was fed through a breaker panel, then would the circuit breaker count as the disconnect switch?

Yes per 28-600 to 28-604

If the compressor motor wasn’t thermally protected, what would be the most cost effective method of providing this?

A manual motor switch with integral overloads might do it but be careful about whether it will restart automatically.

Thanks in advance. Sorry for the long post.

Bruce


Bruce we never get better when we avoid particular work because we don't know the answer. Glad to see you are trying.

If it were not for the danger presented by moving parts and the need to up size the over current devices then motors would be easy. BTW the on off switch might serve as a disconnecting means. Good luck and stop letting your current abilities determine your future abilities. These are opportunities to expand your competencies. Time to open section 28 and get comfortable but not too comfortable as that can lead to complacency.


#181887 - 11/06/08 12:13 PM Re: Motors [Re: mikesh]  
brsele  Offline
Member
Joined: Jul 2008
Posts: 89
Northern Ontario
FYI- The install went well with no defects.

Another question for Mikesh or anybody else who wants to chime in.
In both the CEC and OESC, rule 28-210 states that instantaneous-trip circuit breakers shall not be used unless part of a combination starter, etc.
So with this install, where the motor has thermal protection and a FLA of 15amps, if it was fed through a regular breaker box, could you protect it with say a 30A circuit breaker (non-time delay) and feed the motor directly with #12 wire?

Thanks... Bruce


#181897 - 11/07/08 05:05 AM Re: Motors [Re: brsele]  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Originally Posted by brsele
I can just feed it with 12/2 and fuse it between 20A up to a max. of 45A.
Correct?

2 core cable?
No earth conductor? whistle


Let's face it, these days if you're not young, you're old - Red Green grin

#181898 - 11/07/08 08:27 AM Re: Motors [Re: Trumpy]  
brsele  Offline
Member
Joined: Jul 2008
Posts: 89
Northern Ontario
Mike,

We don't include the bonding conductor in the cable.
It's a given.
So 12/2 has two current carrying conductors and a bonding conductor.

Bruce


#181976 - 11/13/08 03:47 PM Re: Motors [Re: brsele]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
From Table D-16
Min 18.75 amp wire #12 is good
Mad CCT BR. is 35 amps so your 30 is good
If you used fuses then TD at 25 amps or non- time delay at 45 amps.

Instantaneous circuit breakers don't have thermal trip capabilities so will never trip on overload. The only trip on over-current often a minimum of 6 times the normal value of the breaker or 180 amps for the 30 amp breaker.
No overloads required because the motor is thermally protected. A local disconnect if the equipment is further than 9 meters or cannot be seen from the panel and vice versa.

So since you did not mention the panel location or a local disconnect the rest is good so far. IF the panel is within the mentioned distance or you have a local disconnect then you done good. Next motor will be easier.



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