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240 volt blasts appliances #43976 10/26/04 05:40 AM
Joined: Jun 2004
Posts: 613
S
shortcircuit Offline OP
Member
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.

shortcircuit

Work Gear for Electricians and the Trades
Re: 240 volt blasts appliances #43977 10/26/04 05:47 AM
Joined: Aug 2001
Posts: 7,520
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pauluk Offline
Member
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.

Re: 240 volt blasts appliances #43978 10/26/04 06:48 AM
Joined: Dec 2000
Posts: 4,283
electure Offline
Member
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.

Re: 240 volt blasts appliances #43979 10/26/04 07:37 PM
Joined: Apr 2002
Posts: 914
E
Electric Eagle Offline
Member
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.

Re: 240 volt blasts appliances #43980 10/26/04 10:13 PM
Joined: Nov 2002
Posts: 244
W
wewire2 Offline
Member
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.

Re: 240 volt blasts appliances #43981 10/26/04 11:01 PM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline
Broom Pusher and
Member
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".

Scott35

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!
Re: 240 volt blasts appliances #43982 10/27/04 06:12 AM
Joined: Jun 2004
Posts: 613
S
shortcircuit Offline OP
Member
Thanx for the thread scott35...it 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...

shortcircuit

Re: 240 volt blasts appliances #43983 10/27/04 04:46 PM
Joined: Jun 2004
Posts: 220
T
trekkie76 Offline
Member
A properly sized and connected Grounding Electrode Conductor [Linked Image]

Re: 240 volt blasts appliances #43984 10/27/04 04:54 PM
Joined: Jan 2003
Posts: 4,391
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iwire Offline
Moderator
Quote
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


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: 240 volt blasts appliances #43985 10/28/04 03:49 PM
Joined: Oct 2003
Posts: 156
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dereckbc Offline
Member
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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