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Computer back-up electrical system


Bain
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I'm checking out an office duplex tomorrow morning, and the buyer--who's an electrical engineer--is concerned because when the A/C condenser energizes, the back-up power system for the computers in one office occasionally sounds an alarm. I explained that the load upon condenser start-up can be substantial, but he's convinced the problem is grounding related and suspects the ground rod is installed mostly horizontally in dry soil and that the rod is what's causing the problem.

I told the engineer that identifying this particular condition was beyond the usual scope of an inspection, but that I would look for any glaring flubs. I suspect the problem may simply rest within the brand and/or settings of the back-up power system, but wondered if anyone had ever dealt with something like this before.

John

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Hi,

I think your electrical engineer needs to go back to engineering school. There isn't any current carried on the equipment grounding conductors or the equipment grounding electrode unless there's something wrong with the grounded (neutral) conductor's path back to earth, so why would the ground rod make any difference? I think Scott's cause is plausible.

OT - OF!!!

M.

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Originally posted by Bain

I'm checking out an office duplex tomorrow morning, and the buyer--who's an electrical engineer--is concerned because when the A/C condenser energizes, the back-up power system for the computers in one office occasionally sounds an alarm. I explained that the load upon condenser start-up can be substantial, but he's convinced the problem is grounding related and suspects the ground rod is installed mostly horizontally in dry soil and that the rod is what's causing the problem.

The ground rod has nothing whatsoever to do with the day-to-day operation of the electrical system. If you were to remove the ground rod entirely, it would make no difference to the problem you've described.

I told the engineer that identifying this particular condition was beyond the usual scope of an inspection, but that I would look for any glaring flubs. I suspect the problem may simply rest within the brand and/or settings of the back-up power system, but wondered if anyone had ever dealt with something like this before.

John

On startup, the AC system draws a huge amount of current for a very short period of time. This is causing a momentary voltage drop and the back-up system is reading this as a power loss.

The back-up system might be adjustable. That is, he might be able to have someone adjust the threshold at which the system cuts in.

Another possible cure would be to have the heating contractor install a soft-start kit on the compressor to lessen the initial power draw.

- Jim Katen, Oregon

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Originally posted by Jim Katen

Another possible cure would be to have the heating contractor install a soft-start kit on the compressor to lessen the initial power draw.

- Jim Katen, Oregon

What's a soft start kit? My AC compressor makes the breaker sound like a hammer in the electrical panel.

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I read you loud and clear vis a vis the grounding rod having nothing to do with voltage drop, and thought the same thing. But then I told myself, "He's an electrical engineer . . . He know's more about this than I do."

I'll humbly borrow from you all and seem much smarter than I am tomorrow. Thank you.

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Originally posted by Bain

I read you loud and clear vis a vis the grounding rod having nothing to do with voltage drop, and thought the same thing. But then I told myself, "He's an electrical engineer . . . He know's more about this than I do."

I'll humbly borrow from you all and seem much smarter than I am tomorrow. Thank you.

Well before you borrow from me, allow me to correct my error. It's a hard-start kit, not a soft-start kit.

Kurt, as I understand these things, they're basically a capacitor-based booster system for the compressor motor. They increase starting torque and reduce voltage drop.

Of course, John, you should recommend that they investigate the incoming power. If there's a loose or corroded connection on one of the ungrounded conductors, even as far back as at the transformer, that could increase the voltage drop as well.

One other thought. AC compressors often draw more current as they go bad. This one may be near the end.

In any case, there's a good deal of investigation to be done.

- Jim Katen, Oregon

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That's pretty much what I told him, Jim, and added that I know a thoughtful, responsible electrician. I asked about the age of the compressor and compared it to those old, belt-driven furnace blower-motors that always seem to dim the lights, but the guy was clueless about the compressor's age.

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Originally posted by Jim Katen

One other thought. AC compressors often draw more current as they go bad. This one may be near the end.

- Jim Katen, Oregon

Funny you should say that. My 2 year old Carrier 12 Seer SilentSystem beauty just blew out, and I hardly ever turn it on.

The last couple times it started up, you'd have sworn there was a troll in the electrical panel hitting the breaker w/a hammer.

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Originally posted by kurt

Originally posted by Jim Katen

One other thought. AC compressors often draw more current as they go bad. This one may be near the end.

- Jim Katen, Oregon

Funny you should say that. My 2 year old Carrier 12 Seer SilentSystem beauty just blew out, and I hardly ever turn it on.

The last couple times it started up, you'd have sworn there was a troll in the electrical panel hitting the breaker w/a hammer.

Who installed it? The compressors that Carrier uses are usually extremely durable. I often see them still going at 20, 25 & sometimes 30 years.

If one blew out at two years, I'd guess that someone didn't purge his refrigerant lines very well.

I presume Carrier's warranty is replacing the hardware?

- Jim Katen, Oregon

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Well, but it's fascinating how we all look at things in different ways. The engineer who currently works in the building described above and is now buying it, suspected a grounding problem because his surge protectors have lights on them that say "Improper ground," or "Wiring fault." When I explained that the original two-prong receptacles had been replaced with three-prongers, he just looked at me in stunned disbelief. "Who would do something like that?" he asked.

I told him I see it all the time.

"But it's wrong. What kind of electrician would do that?"

It was amazing, watching his learned, logical mind trying to wrap itself around the idea that someone could be dopey enough to connect the wrong kinds of outlets to the wiring.

As for the power-pack, it beeped and the lights dimmed when the furnace blower energized sans condenser, and I regurgitated the suggestions of my kind respondents to the post, and told the engineer an electrician needed to investigate further.

John

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