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Exception to the rule of grounding.....need answer!!!!

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michaeld

Member
Please help!!! Power tools and electrical equiptment with exposed, noncurrent-carrying metals parts must be grounded. What is the exception to this rule?
 

bennie

Esteemed Member
Re: Exception to the rule of grounding.....need answer!!!!

Tool must be listed as double insulated. UL label with a two wire cord is a good sign. Grounding the enclosure is dangerous.

Bennie
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Exception to the rule of grounding.....need answer!!!!

Bennies right, you should look at 250.114 exception.

I did not remember about the NEC Exception for double insulated tools. :eek:

[ May 11, 2004, 04:55 AM: Message edited by: iwire ]
 

monkey

Senior Member
Location
Arizona
Re: Exception to the rule of grounding.....need answer!!!!

Grounding the enclosure is dangerous.
I know the code forbids grounding of double insulated motors but I don't understand the hazard. What exactly is the hazard?
Thanks, Brian
 

bennie

Esteemed Member
Re: Exception to the rule of grounding.....need answer!!!!

A three wire cord implies the tool is grounded.
 

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
Re: Exception to the rule of grounding.....need answer!!!!

Originally posted by monkey:
Grounding the enclosure is dangerous.
I know the code forbids grounding of double insulated motors but I don't understand the hazard. What exactly is the hazard?
Thanks, Brian
First, where will you attach the equipment bond wire?
Second, you will void the listing

The manufacturer makes the double indulated tools to a standard and they have a dielectric withstand test done.
 

karl riley

Senior Member
Re: Exception to the rule of grounding.....need answer!!!!

I'm curious about this. I've never seen a double insulated tool with a metallic case. Do they exist?

Karl
 

jes25

Senior Member
Location
Midwest
Occupation
Electrician
Re: Exception to the rule of grounding.....need answer!!!!

My sawzall hax a 2 wire cord says double insulated on it and the whole front half is a steel case although it is covered by rubber but the rubber I think is just for grip it slides all around.
 

monkey

Senior Member
Location
Arizona
Re: Exception to the rule of grounding.....need answer!!!!

When I asked about double insulated motors I was thinking particularly of 680-22(a)(4) (99 NEC)which says a double insulated motor shall not be bonded. It doesn't say need not be bonded, it says shall not be bonded. By the way, what does a double insulated pool motor look like anyways? Do they even have exposed metal parts?
Brian

[ May 12, 2004, 11:36 PM: Message edited by: monkey ]
 

bennie

Esteemed Member
Re: Exception to the rule of grounding.....need answer!!!!

A lot of tools and equipment are double insulated with metal enclosures. The metal is necessary for physical protection.

The first clue is the tools will not have a grounded cord or attachment plug. Garbage disposals and trash compactors have metal enclosures and frames.

I got hammered by two of the professional code instructors, Joe Tedesco and R Keis, for my view on grounding. My view is substantiated in many cases.

50 years ago, I protested the emphasis on grounding and the cost. Equipment grounding, in many cases, is still a big waste of money and resources.
 
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