For "generic AF study, 480V, LV Swgr (UL1558). What working distance do people customarily use for the "front" of the equipment? 18 or 24 inches. I always thought 18 was used for the rear and 24 for the front unless a specific task lowered it to 18".


So 18 or 24, or something else?

And if you recommend 18, when is 24 used for anything?

I use 24".

Mike

We use 24 inches as well. You might find the results of this poll from the forum interesting. The majority of people use IEEE 1584 distances (including LV swgr at 24"). Some did answer "it depends", but unfortunately no one elaborated.

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[quote="Electricidad"]For "generic AF study, 480V, LV Swgr (UL1558). What working distance do people customarily use for the "front" of the equipment? 18 or 24 inches. I always thought 18 was used for the rear and 24 for the front unless a specific task lowered it to 18".

I wonder if you could clarify the question please? As working distance is measured from the source of the arc, I'm not sure why the front or rear of the switchgear would make any difference.

Many thanks, Mike

We use 18" as it's the most conservative and means the electrician should be wearing a higher level of PPE. Compare the difference in incident energy values for the two distances and you'll see it's much lower using 24". The whole point behind this standard to to limit injury from an arc flash. Even using the correct level of PPE, there will likely be some injury to the worker so my view is consider worst case as the default.

We use 24" since most electricians will be using a hand crank or remotely operated racking device to remove the breaker from the cubicle. Most electricians will not go inside move the shutters open and measure the voltage. This is extremely dangerous!

I think why some folks use 18" for the rear is because an electrician can easily remove a rear panel and measure the voltage with a hand held meter. Performing this task means the working distance is 18" (average length of a human arm when extended.)

Another issue, it is just as important to use HCB on any equipment you insert, drawout breakers, mcc buckets and bus plugs.