replace a 3p motor in a old builidng which no grounding 5

[tgheng]

Hi, I was asked to replace a new 3phase 208 Voltage,10hp motor to a old one. But unfortunatly, the old feeder to control panel no grouding,so how can I grunding?, befor the old motor no grunding still worked long time,Can I igord the grunding in this situation? Thank so much for reply.

 

[dpc]

Is the feeder in a metallic conduit? That can serve as an equipment grounding conductor in many cases.

 

[tgheng]

Hi, Dpc:
Thanks so much for reply. Yes, the feeder is metallic conduit,but I want to know whether the inspector will approal or not as per the code if we assume the feeder conduit will serve as a grounding. Since We installed a lot new feeder with EMT,it is metallic, but we still need a grounding wire inside the EMT.

 

[roydm]

If it's screwed conduit it should be OK but I would hate to rely on EMT.
If the motor is near a mass of metal that is grounded I would consider bonding the motor frame to that also.
Roy

 

[rockman7892]

Per section 250.118 of the NEC, both rigid and EMT conduit can be used as an acceptable means of and EGC as dpc mentioned above.

I would think that with these being listed as acceptable means in the NEC, that inspector would have no problem approving them.

 

[waross]

Similar rules in Canada.
EMT may be used, Rule 10-804, (d) subject to some exceptions.
Watch your connection to the motor. Flex is not acceptable for grounding. You may not transition directly to flex unless there is a grounding conductor oin the EMT
You may, however, use a junction box or condulet to transition from EMT to flex and run a grounding conductor in the flex from the motor to the box or condulet.
Rule 10-618 (3)
If this building is over 50 years old, and the EMT is coupled and connected by "indent" fittings, they may not be acceptable for grounding.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[TurbineGen]

If your problem is getting it inspected, Metallic conduit is accepted by NEC, but if the conduit is exposed to the elements I wouldn't recommend it. The joints of the conduit increase in resistance as the conduit deteriorates and in an old installation, the connection to ground may not be sufficient. The NEC suggests using an electrical joint compound as a lubricant to keep the joint impedance low and protect from corrosion. Especially in the case of strong fault, the high resistance will rapidly heat and arc. If this happens where the conduit is buried in concrete, the concrete can explode.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[tgheng]

Hi, guys, Thanks very much for reply and gave me so valuable help. I am very glad to hear from you. This is first time I visit this forum and I am very happy you all are so nice . Merry Christmas and Happy New year!

 

[waross]

Welcome to the forum tgheng.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tgheng]

Hi, Waross, Thank you so much!

 

[sreid]

As a last resort, can you drive in a grounding stake?

 

[tgheng]

Hi, Sreid,thank you for your ideal, I am sure your ideal will be ok if I have no choice.
In this old building,I just did exactly as Waross advised; wired a ground inside the flex from motor to the box/control panel.