4 or 7 Throws of the Hand

[iwire]

I have another question for all of you.

You have a service that consists of the following;

A utility transformer feeds underground to main lug only switchgear.

In that switchgear are 5 disconnects and over time 2 more disconnects have been tapped off the bus bars and mounted to the wall beside the switchgear.

We now have a service that feeds a total of seven disconnects, none of these feed a fire pump.

Here's the thing only 4 of these disconnects control loads in this building.

The three other disconnects control underground feeders to separate structures.

So pass or fail?

4 throws of the hand and the entire building is dead.

 

[bwilson]

Re: 4 or 7 Throws of the Hand

FAIL. 230.71

 

[paul]

Re: 4 or 7 Throws of the Hand

Fail, same reference.

 

[iwire]

Re: 4 or 7 Throws of the Hand

It is planed that this service gear will be replaced with one with a main.

[ April 29, 2005, 05:19 PM: Message edited by: iwire ]

 

[bphgravity]

Re: 4 or 7 Throws of the Hand

From the standpoint of safety, what is the point of only permitting the six disconnects? I have researched this issue in search of the history and intent of the requirement. In most cases, the answer I get is that emergency officials need to be able to quickly remove all power to a building or structure and therefore six throws of the hand is the limit.

What happens at 7? or even 8? I cannot find any documentation or substantiation that indicates the number of "six" disconnects as being some magic limit, nor have I been able find any documented cases of loss of life or property as a result of buildings or structures not in compliance with the six disconnect rule.

And considering that 230.72(A) does not specify and actual dimensional length to define "grouped", it could be conceived that 7 "closely" grouped service disconcects can be shut off faster than 6 "widely" grouped disconnects. Couldn't it?

 

[iwire]

Re: 4 or 7 Throws of the Hand

Bryan

I think you raise some interesting issues.

Many of the buildings we work in have one main however beyond that there may be multiple UPS and generates spread throughout the building.

As soon as the emergency official(s) kill that power many other power sources may come on line.

 

[pierre]

Re: 4 or 7 Throws of the Hand

Bryan
My only answer to your question is that the number had to be picked, and six is the number.
It could have been 7, 8, 9 etc... but they stopped at six.

Why 5 feet for the distance of the GEC connection to cold water?

Why a 15 amp breaker, and not a 17 amp breaker?


Who came up with the size of conduit?
Where did duplex receptacles come from?

 

[charlie]

Re: 4 or 7 Throws of the Hand

Proposals are submitted with a distance, number of operations, etc. The panel accepts 25 ft and then the next cycle gets a lot of proposals to increase it to 50 ft, 75 ft, and 100 ft. After looking them over, they settle on 75 ft as a compromise and almost everyone is happy. Later, there is a problem with 75 ft and several proposals come in to go back to 50 ft.

What I am trying to say is that numbers are many times arbitrary unless there is some calculations that go with them.