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#43976 - 10/26/04 03:40 AM 240 volt blasts appliances
shortcircuit Offline
Registered: 06/27/04
Posts: 608
Loc: massachusetts
I went on a service call where the neutral was lost going to a house which sent 240 volt through the 120 volt branch circuit wiring. Well the homeower is out 2 TV's, a VCR, a stereo, and a microwave.They all seem to be damaged by the 240 volt surge.

Does anybody know how much damage may have been caused to the TV's and other appliances from the 240 volt surge?I'm thinking that maybe just a power supply transformer fried.

I wanted to tell the customer if the appliances were worth getting repaired.

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#43977 - 10/26/04 03:47 AM Re: 240 volt blasts appliances
pauluk Offline
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
It will depend very much on the design of the equipment. Some TV power supplies have an overvoltage "crowbar" circuit to protect the rest of the circuitry, in which case some work on the power supply components should restore operation, but it's not universal.

You could expect to find damaged filter capacitors and quite possibly burned out transistors and integrated circuits in bothe the TV and the audio equipment. If the microwave oven is a modern type with digital control, then the main board may well be shot due to the overvoltage.

Unfortunately it's impossible to be any more precise without actually testing the equipment to see what's been fried.
#43978 - 10/26/04 04:48 AM Re: 240 volt blasts appliances
electure Offline

Registered: 12/24/00
Posts: 4259
Loc: Fullerton, CA USA
Keep in mind that probably none of the 120V appliances actually received 240V.

The circuit becomes a series circuit when the "noodle" is lost, and the voltage seen by anything on either ungrounded leg will be dependent on the load attached to the other.
#43979 - 10/26/04 05:37 PM Re: 240 volt blasts appliances
Electric Eagle Offline
Registered: 04/20/02
Posts: 914
Loc: Alpharetta, GA
Electure is right about the voltage. What you normally get is more like 145 on one leg and 95 on the other. Together they will both always add up to 240. The more load put on 1 leg(voltage drops), the other leg goes up the same amount the other drops.

It's actually quite interesting to witness how the lights get brighter when a load is appied to a circuit on the opposite leg.
#43980 - 10/26/04 08:13 PM Re: 240 volt blasts appliances
wewire2 Offline
Registered: 11/14/02
Posts: 244
Loc: California
If the problem was on the utility side, they may be able to reimbursed thru the utility's insurance co. If so, just call and request a form.
#43981 - 10/26/04 09:01 PM Re: 240 volt blasts appliances
Scott35 Offline

Broom Pusher and
Registered: 10/19/00
Posts: 2707
Loc: Anaheim, CA. USA
Take a look at the thread Losing Neutral , as there is quite a bit of information regarding the scenario.

Be sure to check out all the replies in that thread, as there will be key points which cover the "Whys" and "Hows", as well as the "What Happens".


p.s., click on the underlined text "Losing Neutral", as it is a hyperlink! It will open the discussion thread in a new page, so this page stays open too.
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#43982 - 10/27/04 04:12 AM Re: 240 volt blasts appliances
shortcircuit Offline
Registered: 06/27/04
Posts: 608
Loc: massachusetts
Thanx for the thread shed some light on the situation.

Does't sound like there will be much to salvage from pauluk's post.

Is there any protection that could be added at the main service to a dwelling to protect against a lost neutral...

#43983 - 10/27/04 02:46 PM Re: 240 volt blasts appliances
trekkie76 Offline
Registered: 06/19/04
Posts: 220
Loc: baileyville, maine, usa
A properly sized and connected Grounding Electrode Conductor
#43984 - 10/27/04 02:54 PM Re: 240 volt blasts appliances
iwire Offline
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
A properly sized and connected Grounding Electrode Conductor

I have to disagree with that.

The only electrode that might keep a lost neutral from causing voltage imbalance would be a metal water pipe that is electrically continuous with your neighbors neutral.

If that is the case you have only postponed the problem till someone separates the pipe and gets a shock while doing so.

The other types electrodes, rods, plates, concrete encased etc. will do very little to keep the voltage balanced with a lost neutral.

Bob Badger
Construction & Maintenance Electrician
#43985 - 10/28/04 01:49 PM Re: 240 volt blasts appliances
dereckbc Offline
Registered: 10/08/03
Posts: 156
Loc: Tulsa, OK
Trekkie76 said "A properly sized and connected Grounding Electrode Conductor"

I seriously doubt it. The GES impedance would have to be less than .1 ohms to do that. Or as Bob said; an alternate path through a common metallic water pipe.

Edited for spelling errors.

[This message has been edited by dereckbc (edited 10-28-2004).]
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