APC hums (buzzes) when hair dryer is run in another room

Possibly knob and tube? Or steel conduit?

Does the dryer have a variable heat control?

Probably not. Can you meter the supply?

On Wed, 22 Nov 2006 20:27:10 +0000, BE Has Frothed:

The APC should be grounded. You're sure it isn't switching to battery?

To the extent that such a switch would be indicated by the beeping of the unit, I am positive that it is not.

I would love to be able to ground it properly, but this is not possible. I figure it is better than running the computers themselves ungrounded and subject to this house's "dirty" electricity. Since I lost a computer 7-8 years ago to the abuse this house's electricity inflicted upon its power supply, I have made it a policy to have a UPS for everything I care about: TV, wireless internet base station and DSL modem, plus all three of our computers. I think it's better to have these UPS units ungrounded than not at all.

Be

It is copper wire with a very thick braided covering.

Yes.

I have metered one of the outlets in another part of the house and the current seems to average 123 volts. Should I plug this tester into the back of the UPS - is that what you are suggesting?

Be

Single conductor or a jacketed two conductor cable? I've seen knob and tube wiring as you describe. When I got down to the actual conductor, it was something like 20 gauge...very small; and this was house mains wiring.

I think he's suggesting that the load of the dryer (these can consume well over a kilowatt on high power settings) might be pulling down the supply voltage. Try again with the dryer running. It might be on the same overloaded circuit.

jak

Ground the UPS (run a wire down the stairs to the kitchen if you have to) and see if the buzz goes away when the hair dryer is on. If it does not, then start looking elsewhere (temporarily try a different UPS?). If the buzz does go away, then its a grounding problem...either find a UPS that works better without a ground, figuring out how to ground the UPS permanently, or forget it and see what happens.

Dan

Measure the voltage at the outlet the UPS is plugged into while the hair dryer is on, it sounds like the voltage is sagging.

Does it run in steel conduit? If so, that is often (but not always IME) a good ground.

Just a switch (low-med-high) or a dial (0-9)?

No, while there is a niggling doubt that something nasty is happening you are most probably OK.

However your wiring was intended for lighting and very light loads (radio etc). I assume you have gas cooking and heating and not electric. If you have a friendly electrician perhaps he could tell you his opinion of your wiring.

I _think_ we are OK - we have lived in this house for more than 10 years now; if we were overtaxing the circuits they would have done something (logic suggests) to indicate this by now. Only on a couple occasions have we even blown a fuse. Our fuses are the old screw-in type that look like the bottoms of light bulbs.

Be

I hear you, but sometimes people screw with this stuff. Knob and tube is usually fine unless you get an amateur who tinkers with it. Then it is a fire and shock risk.

I think there is a very simple explanation for what is going on.

The hairdryer is putting out a lot of electrical "noise" onto the electrical power line. That noise goes through the wiring and into the front end of the UPC and gets into the UPC power line voltage sensors and is causing them to rapidly cycle on and off, hence the chattering or buzzing sound from the UPC.

I would guess that the dryer and the UPC are on the same circuit, or at least on the same 120V phase, assuming the house does have a 230V input. The noise is most likely being conducted into the UPC, although I would not 100% rule out radiated noise. A simple power line filter on either the hair dryer or the UPC should fix the problem. They are about the size of a pack of cigarettes, plug into the wall and have an outlet into which you plug the appliance. You can also make up a crude filter using ferrite toroidal cores. If you can get hold of a member of the Institute of Electrical and Electronic Engineers Electromagnetic Compatibility Society, they can help you. I am past president of that organization and our members are always interested in these sorts of problems.

H. R. (Bob) Hofmann

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My house is 100 years old. My K&T is 16 gauge. I've replaced all of the power circuits in the house. Only using the K&T for lighting and replaced most of the lights with CFL. The hair dryer is going to take a considerable portion of the lines capacity. Do you know if the fuse is correct for the wiring? Even if it is correct a bad connection can cause heat and fire without blowing fuse. Not only are the lines light duty, to say the least, little thought was given as to where power needed to be distributed. Especially by modern standards. The outlet we used for coffeemaker and toaster was 10' from fuse box but electricity came through 60' wire.

Not trying to scare you but you really should know what your dealing with regardless of what's causing the noise. What you describe doesn't sound like arcing but who knows. House fires are almost as common as major crimes. Do you lock your doors at night?

Does it only do it when the hair dryer's on low heat ?

I've come across something similar *once only ever* and it was also bad wiring.

The hairdryer uses a diode for low heat and this creates a DC content on the AC line.

You need your wiring replaced.

Graham

On Thu, 23 Nov 2006 02:05:00 +0000, BE Has Frothed:

My home lacks 3 conductor wiring. I added a ground to a few outlets (computers, ham equipment uninterruptable supplies, shop electronics) by driving a 6" copper rod at each end of the house into the ground and then adding them to whatever circuit I wanted. This comming spring I will upgrade the service to 3 wire, 100 amp as it stands right now I have 4 round fuses for the entire home (2 bedroom brick with basement and attic)60 amp.

On Thu, 23 Nov 2006 02:39:34 +0000, Homer J Simpson Has Frothed:

Ok what's knob and tube?

-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85.

Michael A. Terrell Central Florida

Try to convince me that was a good idea. My first reaction is to think it would potentially (no pun intended) create a colossal ground loop.

APC is probably sensing all the spikes and noise being generated by the hair dryer, that is across the ac line.

apc units can be so well designed that they will detect any non-pure waveform that gets induced into the circuit it is connected to. they usually switch to battery whenever this happens, they do it so quickly u nevr notice unless it is a repeated event, such as a 1.2kw hair dryer and its cheap motor loading the wires in your house.

while it wont cause you any problems, it is an indication the house wiring is inadequate for the powerful hair dryer

i am surprised the APC even works without a proper ground circuit! most will fail to start when ungrounded.

assume).use you any problems,

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