Why one service drop?

[Julio Bro]

Hi:

I asked Mike this and told me to come here.

Using as reference the 2002 NEC and Vol. 1 of the guide, article 230 indicates structures should have 1 service drop only, with some exceptions accompanied by an info plaque. Neither book explains why and that's what we want to know.

So, why is it that the NEC indicates that structures should have 1 service drop only? A friend says the main reason is safety, but we need a deeper explanation.

Also, the conditions or safety reasons that oblige the 1 service drop only rule, don't apply to multiple EGs in structures/buildings? I think the Special Condition of Emergency Power allow the installations, but we need a deeper explanation.

 

[Hendrix]

Hi:

I asked Mike this and told me to come here.

Using as reference the 2002 NEC and Vol. 1 of the guide, article 230 indicates structures should have 1 service drop only, with some exceptions accompanied by an info plaque. Neither book explains why and that's what we want to know.

So, why is it that the NEC indicates that structures should have 1 service drop only? A friend says the main reason is safety, but we need a deeper explanation.

Also, the conditions or safety reasons that oblige the 1 service drop only rule, don't apply to multiple EGs in structures/buildings? I think the Special Condition of Emergency Power allow the installations, but we need a deeper explanation.

Ask your fire dept.

 

[480sparky]

Ask your fire dept.

That's my thinking as well... it's a FD-driven thing. They want to be able to know they've turned power off by having only one service to worry about. If there's more, they end up wasting time looking for others instead of stomping out the fire.

 

[srisser]

If I understand NEC 230.2 correctly along with all of the interpretation from the electrical inspectors in our department, the predominant reason for only allowing one electrical service is for the sake of safety during an emergency. If there is a fire or emergency in the structure, the FD can disconnect all of the electrical power or simply pull the meter (which usually happens anyways) at one location. They do not have to worry about entering a structure with conductors that may be energized. Additionally, they do not have to waste time trying to find all of the electrical service locations.....except for those that are working on their behalf....fire pump....emergency/standby providing power to emergency lighting, alarms, exit signs and elevators....critical branch in health care facilities.

There are additional conditions that would permit additional services...emergency and standby systems....fire-pumps.....large demand requirements. It is rare (but some installations do require) that our Chief Building Official (AHJ under the NEC) permits an additional service under 230.2(B).....most installations in our jurisdiction can be adequately served by the power co with one electrical service.

 

[altarengineering]

I agree, with the previous few post. It is my understanding that safety, Primarily of the FD is the driver for this rule. I do know of a case were the facility had its own fire protection system, and the inspector forced the company and the service provider to install two transformers and two service entrances. One dedicated to the fire protection system. So there is one exception...

 

[don_resqcapt19]

That's my thinking as well... it's a FD-driven thing. They want to be able to know they've turned power off by having only one service to worry about. If there's more, they end up wasting time looking for others instead of stomping out the fire.

I am not aware of any fire department that looks for the electrical disconnect(s) before fighting the fire, unless electrical equipment is directly involved in the fire.
The following is from this Army Technical Manual on page 15-3 and 15-4.

The following discussion
is based on using water at 689 kPa (100 psi),
water resistance of 1,524 ohm cm (600 ohm in.), and a
current of 3 mA or less in the fire hose stream. ...Solid
stream nozzles less than 32 mm (1.25 in.) in size can be
used on live low-voltage (less than 600 V) circuits at all
distances greater than 1.5 m (5 ft).

 

[480sparky]

I am not aware of any fire department that looks for the electrical disconnect(s) before fighting the fire, unless electrical equipment is directly involved in the fire.
The following is from this Army Technical Manual on page 15-3 and 15-4.

I'm not saying local FDs put the requirement in..... it's due to the FD industry as a whole that did.

It's the same logic drop-in troffers are required to be supported independent of the grid.... they don't want them falling on the FFs while inside the structure.

 

[dcspector]

It's the same logic drop-in troffers are required to be supported independent of the grid.... they don't want them falling on the FFs while inside the structure.

Ken I see what you are saying but that is a seismic and grid manufacture requirement.

 

[Twoskinsoneman]

What a drag it would be if you were crawling along the floor of a smoke filled building trying to get out when all of sudden all the lights go out. :smile:

 

[Julio Bro]

Alright, the issue and rule is Fire Department driven and eventually applied; thanks.

The second part of my questioning was not answered. What about multiple emergency generators? Is there no problem with this, multiple transfer-switches, and different circuit panels from the generators? What does the FD says about this?

 

[daleuger]

Ya that would be my guess too. One spot to kill the building. It's kind of along the lines of having hurricane clips and tying in drop in light fixtures. Also FD driven that way when they come in and start swinging axes it all doesn't rain down on their heads. That's my understanding at least.

 

[dcspector]

Ya that would be my guess too. One spot to kill the building. It's kind of along the lines of having hurricane clips and tying in drop in light fixtures. Also FD driven that way when they come in and start swinging axes it all doesn't rain down on their heads. That's my understanding at least.

Show me in the code besides 410.16(C) where it says ( now local amendments and seismic concerns yes ) where the simple lay in luminaires must be independently supported from grid. BTW... The New educated advanced FD does not go in swinging axes like the old days.

 

[daleuger]

Show me in the code besides 410.16(C) where it says ( now local amendments and seismic concerns yes ) where the simple lay in luminaires must be independently supported from grid. BTW... The New educated advanced FD does not go in swinging axes like the old days.

I've argued that same point over and over and over till I was blue in the face. I think it's overkill and an enormous waste of time myself, but I eventually let it go. If it must be done....send the helper.

 

[don_resqcapt19]

What a drag it would be if you were crawling along the floor of a smoke filled building trying to get out when all of sudden all the lights go out. :smile:

If the building is smoke filled, it really doesn't make any difference if the lights are on or off...you can't see them:grin:

 

[don_resqcapt19]

Ya that would be my guess too. One spot to kill the building. It's kind of along the lines of having hurricane clips and tying in drop in light fixtures. Also FD driven that way when they come in and start swinging axes it all doesn't rain down on their heads. That's my understanding at least.

As a firefighter I would be a lot more concerned about the grid coming down than the fixtures coming down. My gear will most likely protect me from the fixtures, but I may become so tangled in the grid and the wiring laying on top of the gird that I can't exit the building before my air runs out.

 

[don_resqcapt19]

Show me in the code besides 410.16(C) where it says ( now local amendments and seismic concerns yes ) where the simple lay in luminaires must be independently supported from grid. BTW... The New educated advanced FD does not go in swinging axes like the old days.

Actually firefighters probably put more openings in the building walls, ceilings and roofs than in the old days. Ventilation is a very critical part of fire fighting and protecting the interior firefighters. With a drop ceiling it would be unlikely that a firefighter would remove a fixture on purpose or swing an ax at the grid. A pike pole or water stream would be used to open that type of ceiling.

 

[Julio Bro]

People, people...what about my question? Is there a rule in the NEC or the Safety Code about multi-generator installations, particularly condo buildings?

 

[dcspector]

People, people...what about my question? Is there a rule in the NEC or the Safety Code about multi-generator installations, particularly condo buildings?

Julio...Sorry....

Hi Rise?......Are you asking if more than one Generator is required?....IBC 2702 and 403 cover stand by power systems along with NFPA 110 and 111

 

[iwire]

People, people...what about my question? Is there a rule in the NEC or the Safety Code about multi-generator installations, particularly condo buildings?

Sure, but you asked about services and services are always supplied by the utility (See the Article 100 definition of "Service"


The supplies from on site generators are "feeders" and the rules for feeders that supply buildings or structures can be found in part II of Article 225.

You should specifically look at 225.30(A).

 

[Julio Bro]

Will check there.

Thanks.