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 Post subject: 18" working distance on 2400V MCC's? 36" on swgr
PostPosted: Tue Oct 12, 2010 8:36 am 
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I have just noticed that the default working distance (apparently based on IEEE 1584) is 18". That slipped by unnoticed in the past.

But 2400V "switchgear" defaults to 36" working distance. That seems like quite a difference in working distance. And also that will result in substantial difference in calculated exposure. Especially considering some workers might not recognize the difference between switchgear and motor control centers at this voltage level.

It seems preferred to standardize on 24" and avoid possibly lethal confusion(?)

Any comments?


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PostPosted: Mon Oct 18, 2010 4:55 am 
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I'd rather the jump be made to the higher instead of dropping the 2,400V down by a foot...

Not sure about your area, but the clearances in front of gear here needs to be 1 meter (about 39") up to 800 Amps. Over that it has to be 1.2 meters (about 47"). That is for working area , not considerring Arc Flash...


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PostPosted: Mon Oct 18, 2010 5:56 am 
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Gary B wrote:
I have just noticed that the default working distance (apparently based on IEEE 1584) is 18". That slipped by unnoticed in the past.

But 2400V "switchgear" defaults to 36" working distance. That seems like quite a difference in working distance. And also that will result in substantial difference in calculated exposure. Especially considering some workers might not recognize the difference between switchgear and motor control centers at this voltage level.

It seems preferred to standardize on 24" and avoid possibly lethal confusion(?)

Any comments?


IEEE 1584 Section 4.8 Table 3:
LV switchgear = 610 mm (24 inches)
5 and 15 kV switchgear = 910 mm (36 inches)

I have seen a few programs default to 18 inches and it is left to the user to change it. I assume the reason is to be conservative but 18 inches for switchgear can quickly have you in some pretty "impressive" PPE.

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PostPosted: Thu Jan 13, 2011 1:55 pm 
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I have some 2400V Allen Bradely bolt in contactors that are 18" from the disconnect switch to the bus. On our old draw out contactors you are definitely 24" from the bus.

You need to consider the working distance from the energized conductors, it can be different for some pieces of equipment.


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PostPosted: Thu Jan 13, 2011 3:11 pm 
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Jaredx9 wrote:
I have some 2400V Allen Bradely bolt in contactors that are 18" from the disconnect switch to the bus. On our old draw out contactors you are definitely 24" from the bus.

You need to consider the working distance from the energized conductors, it can be different for some pieces of equipment.


Quite correct. Default data is exactly that... default.

Here is one not too many people think about.

When the back of equipment is labeled assuming it can be accessed from the back while energized, is the same label on the front placed on the back?

On the front label the assumption is the bus structure is towards the back (24", 36" etc.) On the back of the equipment the same bus structure is.... you guessed it ...a lot closer than the front.

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