ECN Forum
Posted By: lamplighter external means for disconnect - 10/20/05 02:37 AM
When I was living in Fl., I used to have to adhere to the N.E.C. as well as the S.F.B.C.(south florida building code).
S.F.B.C. is in place due to hurricane ratings and the like.
On any service, you had to leave an external means of disconnect and the meter did not qualify as such.
This meant a main breaker mounted usually to the side of the meter can with an offset nipple before going on to the distribution panel inside.
In Michigan, I ran into something I had never seen in Fl., i.e. buss riser system.
The problem is that a buss riser system has no external means for disconnect unless you mount a shunt-trip which is never called for by the architect up here.
My father-in-law is a fireman for over 35 years and he says that in case of fire, the firemen sever the service drop near the pole. The main problem I see with this is that when it comes to an industrial fire in a small manufacturing facility, the fireman on the ladder might be cutting a 5000 amp service or even bigger while there is a load on it, with water spraying everywhere, in the dark, and trying to see through a possibly soot covered face shield while doing it.
Does this sound unsafe to anyone else?
Posted By: resqcapt19 Re: external means for disconnect - 10/20/05 03:00 AM
First very few firefighers are qualified to cut energized serivce conductors, and then most likely don't have the correct PPE to do it safely. Second, it might not be very wise to cut the power at the pole because it could be feeding the building fire pump. Third, the building "pre-plan" that should be done by the fire department for commerical and industrial building will show the locations of all of the building utility service disconnects. This makes it easy to use the normal building disconnect to kill the power in the building, while waiting for the utility to kill the service drop.
Don
Posted By: gfretwell Re: external means for disconnect - 10/20/05 04:58 AM
Alas the SFBC is long gone. The UFBC is the NEC (2002 right now) unaltered, statewide.
Posted By: lamplighter Re: external means for disconnect - 10/20/05 03:55 PM
---"This makes it easy to use the normal building disconnect to kill the power in the building, while waiting for the utility to kill the service drop."---

The problem I see with this is that the fire may very well prohibit the firemen from getting to the disconnect without having to spray large amounts of water on the energized switchgear, bussrails, etc.
The main building disconnect could very well be the source of the fire and I wouldn't want to be the one to have to spray water on an energized 5000 amp main.
I simple little shunt trip could solve some of the problems here but still wouldn't kill the power on the line side of the main.
I think that for once in Fl.'s life, they actually had it right.
An external means for disconnect sounds like a good idea to me.
Posted By: macmikeman Re: external means for disconnect - 10/20/05 04:30 PM
I am taking a wild guess , but perhaps the reason that exterior disconecting means are not so popular on buildings in plenty of area's in the country is because the fire crew might also need to shovel a bunch of snow away in order to acess the thing.
Posted By: gfretwell Re: external means for disconnect - 10/20/05 05:02 PM
I suppose all fire fighters are not created equal but the guy I saw pull a meter (with his axe) did it quickly and was pretty far away from the arc. It came out in one fluid motion with his back to it and moving away.
A fireman in his running gear is fairly well protected anyway, at least as far as a typical dwelling load is concerned.
Posted By: resqcapt19 Re: external means for disconnect - 10/20/05 05:23 PM
Quote
A fireman in his running gear is fairly well protected anyway, at least as far as a typical dwelling load is concerned.
The face protection, and even the normal fire gear does not provide suitable protection for arc flash conditions.
Don
Posted By: resqcapt19 Re: external means for disconnect - 10/20/05 05:55 PM
It is not uncommon to use water fog on energized electrical equipment. Look here
Posted By: gfretwell Re: external means for disconnect - 10/20/05 06:04 PM
Way back in the olden days when I was a sailor (65-71) they had us using low velocity fog on just about everything. The principle is you are cooling the fire off to below ignition temp.
Posted By: lamplighter Re: external means for disconnect - 10/20/05 06:50 PM
I'm not really concerned with the dangers of a dwelling load as much as a wharehouse or manufacturing facility.
A dwelling has an external means even if it's not considered so by local codes. (the meter)
It's those building with a bussriser system or equivalant that I'm mainly talking about here.
Would anyone here want to be the one to sever a 5000 amp, 480v. service drop with an axe or bolt cutters while there is a possible load on it?
I'm sorry, but, an axe handle or fiberglass handles on a pair of bunny guns just wouldn't give me much confidence when there's a possibility of a 4000 amp load or even greater on the service drop conductors.
Posted By: mamills Re: external means for disconnect - 10/20/05 07:41 PM
In my fire department, it was common practice a few years ago to routinely pull the meter when a service disconnect needed to be made, in lieu of a real switch. Usually, this went well, except for a couple of occasions when the glass housing around the meter was also broken. I will say that, thanks primarily to the members of ECN (and some of the horror stories y'all related here), I was able to discourage this practice a couple of years ago. The normal firefighting gear - boots, leather gloves, turnout coat and pants, and a helmet with an open face shield - is a very poor substitute for proper PPE. Nowadays, we simply proceed with extreme caution when access to an interior disconnect is risky, or has been compromised by the fire. If the fire has burned out the service conductors to the building, we secure the area where the conductors have fallen, or we move them with an insulated "hot stick" (the same type used by the POCO. with the exception that we never use ours for opening primary disconnects on poles) to a remote area.

We had a fire many years ago at a local auto dealership, in which the fire actually originated in the electrical service equipment inside the building. There being no disconnect switch outside, we protected the remainder of the building while the electric equipment continued it's meltdown until it finally blew the primary fuses on the pole. The new electric service sports a nice 600 amp disco on the outside.

Mike (mamills)

[This message has been edited by mamills (edited 10-20-2005).]
Posted By: lamplighter Re: external means for disconnect - 10/20/05 08:29 PM
Thanks for the reply Mike,
It's nice to see that I'm not carrying on about a moot point.
It just makes sence to have some means for disconnect on the outside or atleast in an enclosed switchgear room accessible from the outside.
In my area of the country, we have many manufacturing facilities where an outside disconnect would not only be handy but, could actually reduce the risk to those firemen who have enough to worry about while doing their job.
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