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Joined: May 2001
Posts: 717
G
Member
Boy have I had, and had, and had, the argument about Natural Gas. When I got my present job I noticed we had about 80% (of 45 gensets) that were natural gas.

I then checked and we were not installing battery back up lights, so the gens were the back up.

I asked who had approved the use of natural gas since it was a violation. 700-12 states you will have a 90 minute supply on site, and natural gas cannot meet that requirement. I got no reply, but did notice they quit fighting me about diesel generators. [Linked Image]

We just went over part of this in this thread: https://www.electrical-contractor.net/ubb/Forum18/HTML/000062.html

In case you can't tell, I don't believe Nat. Gas should be used for emergency backup gens, but limited to NON (Optional) emergency standby use. Should some disaster occur such as earthquake, tornado, or act of terrorism, you will lose the gas pretty quick.

Joined: Jul 2001
Posts: 311
F
Member
One of my men found a defective time delay relay this morning. It's an ONAN brand emergency generator and ATS approx. 25 years old.

Joined: Jan 2003
Posts: 4,391
I
Moderator
Natural Gas is the most common fuel for small to mid sized life safety generators in this area.

A few times we have had to remove diesel sets and replace them with natural gas sets.

This was necessitated because the storage of diesel fuel near wet lands around here is a major problem.

The NEC provides an exception to the on site fuel requirement.

Quote
Exception: Where acceptable to the authority having jurisdiction, the use of other than on-site fuels shall be permitted where there is a low probability of a simultaneous failure of both the off-site fuel delivery system and power from the outside electrical utility company.

I have never heard of the gas being shut down and I guess the AHJ has not either. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: May 2001
Posts: 717
G
Member
iwire,
Glad to hear about your good luck.

When I was at the Prison, an alarm would sound, and we had 20 minutes to switch our boilers to #2 fuel before the gas was shut down. Happened about 4 times a year.

We live in seismic zone 1, the weakest, but we do have 'em occasionally, and the seismic monitors shut it down.

Part of it was shut down during Isabel.

A line rupture some years ago shut it down for days to a significant portion of the region.

I quoted the exception in the post linked, but when I was the AHJ, it was not going to be allowed, and with design review and acceptance, it still won't be allowed.

Joined: Jan 2003
Posts: 4,391
I
Moderator
George If it can be demonstrated that the gas service in a particular area is that unreliable it makes more than good sense not to count on it. [Linked Image]

That is not the case in the area I work, gas service is very reliable.

I did not follow your statement about starting times, the natural gas sets we install fire in less than 3 seconds and if they have not started in 10 they are not going to. [Linked Image]

Of course these units are generally inside a building and have block heaters that keep the water temp above 120 F all the time.

If the water temp falls we get a low temp alarm.

We also set them up to run once a week for 30 to 60 minutes.

One of the company's customers has over 340 of these natural gas units ranging in size from 30 to 100 KW. Right now we have been contracted to go to about 100 of them and connect them to a monitoring station for Gen. Run, Gen. Fail and Power fail.

This will, when done, verify the generator runs when the exercise cycle comes, if not a generator technician will be dispatched. [Linked Image]

These are article 700 generators for a large retail chain in the North East.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Jun 2004
Posts: 220
T
Member
If it is a Guardian/Generac generator, that is is in auto and you know utility is back on, check F1 and F2 fuses to see if thefe it 240vac going out to the generator transformer. If the PCB doesn't "see" the utility voltage return, the genset will keep running.

Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
Just spotting this topic, and reading the 90 minute fuel aspect, and thinking... Well that's 90 minutes of fuel, minimum! Then thinking Natural Gas, it won't go out. Now, I'm remembering a job we did last year, where the gas did go out, and all the time! It was on a busy road, and had a new gas siezemic shut off valve.

Every time a large truck would go by, the gas would shut off! It was required by and provided by the utility. Meant to operate in an earthquake. It had a little ball that would fall off a holder, and into a valve that would shut off the gas. So, I guess natural gas might not be such a wise idea after all.


Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Jun 2004
Posts: 4
N
Junior Member
Most likely it's the PC board.

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