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Old 08-03-2011, 12:00 AM   #1
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Voltage Droop... how much is normal?


Bought a Kill-a-Watt to determine if I should replace my fridge now or later. While it works, I noticed it has a readout for voltage. When the fridge motor is off, it reads 119.9-120.1 volts. Pretty spot on.

When the compressor kicks on, and the microwave is on full power, voltage droops a bit... down to about 113 with a heavy load from other appliances on.

How much droop should one see in the voltage before they get worried?

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Old 08-03-2011, 05:21 AM   #2
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Voltage Droop... how much is normal?


A voltage drop at the refrigerator receptace of that amount means that the drop is in the wires, not in the 'fridge. It may be normal if the kitchen is some distance from the breaker panel, or you may need to tighten up connecctions and also redo the connections at each outlet box to screw the wires onto each receptacle unit instead of relying on the push-in-and-stick (aka backstab) holes in the backs of the receptacles. (Holes where a screw on the side tightens up the wire are just as reliable as screw on connections)

Now if the voltage in the entire panel drops that 6 volts then taking the time to tighten up individual circuits can be procrastinated upon for now. You can get an excellent idea of drop in the at the entire panel by measuring between a dfiferent breaker screw from the 'fridge circuit and the neutral bus bar.

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Old 08-03-2011, 08:03 AM   #3
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Voltage Droop... how much is normal?


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Originally Posted by Thadius856 View Post
Bought a Kill-a-Watt to determine if I should replace my fridge now or later. While it works, I noticed it has a readout for voltage. When the fridge motor is off, it reads 119.9-120.1 volts. Pretty spot on.

When the compressor kicks on, and the microwave is on full power, voltage droops a bit... down to about 113 with a heavy load from other appliances on.

How much droop should one see in the voltage before they get worried?
Is the fridge and microwave on the same circuit? If so, you may want to split them up to their own circuit if it's that bothersome for you. May have been to code when it was wired originally.
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Old 08-03-2011, 11:59 AM   #4
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Voltage Droop... how much is normal?


5% voltage drop is acceptable for branch circuits.
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Old 08-03-2011, 12:53 PM   #5
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Voltage Droop... how much is normal?


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5% voltage drop is acceptable for branch circuits.
Is it really in the NEC? Could very well be. Here in Canada it's 3% for branch circuits (from main panel).
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Old 08-03-2011, 01:01 PM   #6
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Voltage Droop... how much is normal?


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Is it really in the NEC? Could very well be. Here in Canada it's 3% for branch circuits (from main panel).
It is a FPN (Fine Print Note).

3% Feeders
5% Branch circuits
5% Feeder/branch circuit combined.
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Old 08-03-2011, 01:04 PM   #7
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Voltage Droop... how much is normal?


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It is a FPN (Fine Print Note).

3% Feeders
5% Branch circuits
5% Feeder/branch circuit combined.
Good to know
From the CEC:

3% Feeder or branch circuit
5% combined

Last edited by CheapCharlie; 08-03-2011 at 01:06 PM.
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Old 08-03-2011, 11:31 PM   #8
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Voltage Droop... how much is normal?


It's not bothersome to me. It's a fairly old fridge and large microwave, plus lights and other recepts in use when getting that reading.

While it's a late 50s home, previous HO seems to have replaced half the recepts and backstabbed them all without pigtails, so I'm switching them as I go, and retrofitting grounds to each box as work allows and cleaning up the wire mess.

While on the topic, I'm finding that at least half of the Cooper brand decora rockers installed have developed a "pop" and I'm replacing them as I find them. Is this a result of the backstabs or a maybe a bad lot?

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