The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 13
HotLine1 10
Texas_Ranger 8
Trumpy 8
sparkyinak 7
Who's Online
1 registered (LongRunner), 206 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Page 1 of 3 1 2 3 >
Topic Options
Rate This Topic
#43976 - 10/26/04 03:40 AM 240 volt blasts appliances
shortcircuit Offline
Member

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.

shortcircuit

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#43977 - 10/26/04 03:47 AM Re: 240 volt blasts appliances
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
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.

Top
#43978 - 10/26/04 04:48 AM Re: 240 volt blasts appliances
electure Offline

Member

Registered: 12/24/00
Posts: 4226
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.

Top
#43979 - 10/26/04 05:37 PM Re: 240 volt blasts appliances
Electric Eagle Offline
Member

Registered: 04/20/02
Posts: 928
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.

Top
#43980 - 10/26/04 08:13 PM Re: 240 volt blasts appliances
wewire2 Offline
Member

Registered: 11/14/02
Posts: 246
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.

Top
#43981 - 10/26/04 09:01 PM Re: 240 volt blasts appliances
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
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".

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!

Top
#43982 - 10/27/04 04:12 AM Re: 240 volt blasts appliances
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
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

Top
#43983 - 10/27/04 02:46 PM Re: 240 volt blasts appliances
trekkie76 Offline
Member

Registered: 06/19/04
Posts: 219
Loc: baileyville, maine, usa
A properly sized and connected Grounding Electrode Conductor

Top
#43984 - 10/27/04 02:54 PM Re: 240 volt blasts appliances
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
 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

Top
#43985 - 10/28/04 01:49 PM Re: 240 volt blasts appliances
dereckbc Offline
Member

Registered: 10/08/03
Posts: 158
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).]

Top
Page 1 of 3 1 2 3 >



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals