Allowable droop for residential

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hmspe

hmspe

Senior Member
Location
Temple, TX
Occupation
PE
In the Pheonix metro area the utilities provide the service lateral conductors. Typically for a 200A service they use 1/0 AL. Since we are heavily dependant on refrigerated air conditioning, it is common to have all the lights in a house dim when an AC compressor starts.

Is there a standard that utilities must meet as far as allowable droop? At my home office I haven't measured the droop yet, but the UPS systems in the office go off every time the main AC starts. Any suggestions on how to capture the transient accurately with reasonably priced equipment?
 
Re: Allowable droop for residential

HMSPE,
As far as voltage drop goes the electric co. is allowed 5% above or below 120V L to N. This is in Texas. Hope this helps.
Barry
 
Re: Allowable droop for residential

This condition is a voltage sag due to load change. No need to capture the event, it is obvious.

Consult the utility provider. Likely you will have to live with the dimming. Sorry. :p

Good luck.

Bennie
 
Re: Allowable droop for residential

Bennie,

Agreed that this is due to a load change; however, the utility must have some standard they have to meet. They use conductors with a base rating of 120A for a 200A service. 1999 NEC table 310-15(b)(6) would require me to install 4/0 AL minimum if I sized the lateral, and with the ambient here one jurisdiction has upped the minimum to 250 for aluminum. There has to be a standard that allows the conductors to be sized by a utility based on anticipated load, and I can't imagine that standard not having specifications on allowable droop.

I may not be able to get this fixed, but that doesn't mean I shouldn't try, and it can only help if I can quote a spec.

Martin
 
Re: Allowable droop for residential

This is in Charlie the utility guy's play ground.

He will jump on this when he has the time.
 
Re: Allowable droop for residential

Any good multimeter (we us Flukes) with min max capture will suffice for this. As for the UPS; check for the low voltage settings (on some UPS's) that permit you to adjust the low voltage parameters, this will save the battery, and the minimum setting is above the range where most PC's have problems.
 
Re: Allowable droop for residential

As you have figured out by now, The power co.s don't use any code that I have seen. The NEC stated that the max volt drop shall be 5%. Here in So. Cal. we give the power co. 3% and we (inside wireman) get 2%. The reason for the 3% is that the transformers that the utility co. uses have taps in 2 1/2% steps.
I have ben to war many times with our local utility (SDGE) and have a 95% win ratio. The secret is to "stick to your guns!" Thgey will offer to raise the voltage at your house (what happens at night with a light load?) What they will finally do is to increase the wire or tha transformer. fpn: The r3ason that the utility co.'s don't go by the code is "our stuff is serviced and inspected on a regular basis. Most homes and businesses arn't.
So far I have got them to 1) dig up a major street and install another ug run. 2) add a new pole and transformer closer to the address where the problem was reported - (this has happened 3 times)
Most power co.'s are under the reins of the P.U.C.
 
Re: Allowable droop for residential

Voltage drop page 2
They also have an exclusive contract with each city that they serve. To keep these "goldmines" they must provide reliable, safe, and dependable power. They do not want to have anyone complain.

Good Luck!
Honest Mike
 
Re: Allowable droop for residential

I can't believe I did not reply to this one. Most of the electric utilities are under the control of the various state utility commissions. The Indiana Utility Regulatory Commission controls IPL (my company). The rules that cover us are published by the State of Indiana are in a web page.

We generally are permitted to be within 5% of the nominal voltage. There are some exceptions that you can read about if you are interested. The bottom line is that a regulated monopoly can not do whatever they want to do. With the deregulation, I think the same rules would still apply. :)
 
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