MCC Clearance

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ettek

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Hello, My name is Kenneth Lovasz.
I am currently inspecting some equipment manufactured in China to see if it's suitable work use in the US. I have a particular question about this MCC house used on an oilfield drilling Land rig. My question pertains to NEC 1999 (I don't have 2005 yet) Article 110-26. Spaces About Electrical Equipment.
It states that:

Sufficient access and working space shall be provided and maintained about all electric equipment to permit ready and safe operation and maintenance of such equipment. Enclosures housing electrical apparatus that are controlled by lock and key shall be considered accessible to qualified persons.

(a) Working Space. Working space for equipment operating at 600 volts, nominal, or less to ground and likely to require examination, adjustment, servicing, or maintenance while energized shall comply with the dimensions of (1), (2), and (3) or as required or permitted elsewhere in this Code.

Table 110-26(a). Working Spaces

Minimum Clear Distance (ft)
Nominal Voltage to Ground Condition 1 Condition 2 Condition 3
??0?150 3 3 3
151?600 3 31/2 4

Looking at table 110-26(a) it says that the distance should be 42 inches, but I don't know if it applies in this instance.

Less than half of this MCC is accross from a metal bulkhead that is 38.58" away.

This is actually a pretty good MCC and none of the components in the MCC can be accessed while energize without bypassing two interlocks. The connections of the MCC are accessible, however the only reason one would access this while the MCC is energized would be to take amp readings. There is also an Ammeter provided on the front of each MCC can, (Though it's not very accurate). Does an MCC fall under the category as "likely to require examination, adjustment, servicing, or maintenance while energized"? My concern is the 38.58 Inch measurement to the one part of the wall across from the MCC. Does this comply or not?

I have a drawing but do not know how to post it here.
Any help would be greatly appreciated.


[ November 26, 2005, 09:05 PM: Message edited by: ettek ]
 
Re: MCC Clearance

I happen to feel that all equipment regardless if it is likely to be worked on while energized should meet the minimum working space requirements. And not because I am concerned for those that do unnecessary energized work, but becasue it is really hard to perform work on equipment without it and other hazards are present other than shock or arc flash exposure.

That being said, I would be more concerned to know if the equipment has been tested by a nationally recognized testing laboratory here in the US and if any other standards apply to this type of operation in addition to the NEC, if the NEC applies at all.
 
Re: MCC Clearance

HI Bryan
Thanks for you reply, the MCC has been built and conforms to the Chinese CCC standards which are almost identical to IEC 6049-3. Their only fault is that the manufacture failed to install the nameplate with the required data which is required by NEC, IEC as well as the Chinese 7251.3-1997. However the Chinese do not require that the nameplate include maximum branch-circuit short-circuit and ground-fault protection. I am adding this as an acceptance criteria.

To your second point, yes there are also the API and IEC standars. However, for land rigs the standards are not as well defined as they are for offshore operations, ergo, I am using NEC and CFR-29.

I suppose that since the wall cannot be moved I will have to make them install a non-conductive cover?
 
Re: MCC Clearance

I agree with Bryan but I also think installing a sheet of 3/4" plywood would most likely prevent an accidental contact and solve the possible code violation.
 
Re: MCC Clearance

Originally posted by websparky:
I agree with Bryan but I also think installing a sheet of 3/4" plywood would most likely prevent an accidental contact and solve the possible code violation.
Click to expand...
What a great easy and inexpensive solution. :cool:
 
Re: MCC Clearance

Originally posted by ettek:Looking at table 110-26(a) it says that the distance should be 42 inches, but I don't know if it applies in this instance.
Click to expand...
From that statement, I infer that the MCC is rated 480V or perhaps 480/277V. Is that correct? I ask because if the MCC is rated 120/208V, then you only need 36 inches of working clearance.
 
Re: MCC Clearance

Originally posted by websparky: . . . I also think installing a sheet of 3/4" plywood would most likely prevent an accidental contact and solve the possible code violation.
Click to expand...
That is a new one to me. Are you saying that plywood counts as an ungrounded surface, so that having plywood across from the MCC would give you a "Condition 1" installation?
 
Re: MCC Clearance

Originally posted by charlie b:
Are you saying that plywood counts as an ungrounded surface, so that having plywood across from the MCC would give you a "Condition 1" installation?
Click to expand...
IMO that is correct.

Here is the condition 2 text.

Condition 2 ? Exposed live parts on one side and grounded parts on the other side. Concrete, brick, or tile walls shall be considered as grounded.
Click to expand...
That says to me that walls of other non conductive building materials (sheet rock, wood etc.) are not considered grounded surfaces.
 
Re: MCC Clearance

Depending on the conditions, I have suggested to contractors to "glue" the sheetrock right to the
block or masonary surface (a lot less work required). Due to conditions, sometimes they would need plywood. It is easier to paint (not required, just provides better lite reflection) the sheetrock.


I have to say, as I get older, better light is always good :D

[ November 27, 2005, 11:08 AM: Message edited by: pierre ]
 
Re: MCC Clearance

I'm trying to find an exception allowed by the "elsewhere in this code"
The only thing that I could think of would be:
1) If it's a space accessed only by Qualified personel. (Didn't help)
2) The remark in the code stating "likely to require examination, adjustment, servicing, or maintenance while energized shall comply with the dimensions of (1), (2), and (3) or as required or permitted elsewhere in this Code".
The work "Likely" to me is very subjective. There will be no work on energized components as the cans cannot be opened without operating two bypass interlocks. The only time someone will open the edge panels will be to take a voltage measurment in case of equipment failure or to take amp readings. I don't know if this argument will fly.
3)This is a portable structure designed to be moved on trucks so I don't know if there are any exceptions there.
Thanks for your help
Ken
 
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