[Dougie Down]

15 amp receptacle was being replaced. It has three wires- red, black, and white. Power was not turned off. Attached red wire. Attached black wire- big spark. Main breaker flipped. (60 amp service) as well as double 15amp breaker that the circuit is on. Connected receptacle as was before. Now main breaker still flips when 15 amp circuit is flipped on. What could it be? Change the 15 amp breaker?

 

[joecaption]

No way it was wired as it was before if this is happening.
Now there's a dead short.
Add your location in your profile, in the US it should have been 1, white (nutral) 1, black, (Hot) and one bare ground wire.

Look at the old outlet to see if the tab was broken off between the two outlets.
That would mean you have one side hot all the time and one goes to a switch. Connect it without breaking off that tab and it's shorted out.

 

[Dougie Down]

I'm in Ontario, Canada. Forgot to mention the white wire. I will check the tab!

 

[Speedy Petey]

A) WHY THE HELL DID YOU DO THIS LIVE???????

B) Did you look at the receptacle before you took it out?
You would have seen that the tab between the two brass screws are broken off. This is because this receptacle is fed by TWO circuits. The red and black and two-pole breaker should have been a tip off.
You need to break the tab between the two brass screws.

You're in Canada, I assume this is a kitchen receptacle?

 

[Dougie Down]

Just looked at old receptacle. Tab is broken. You saved my butt! I know this is a bad excuse, but panel was not labeled and many computers were on in the house (not my house)

 

[dmxtothemax]

You should ALWAYS do a test to verify that the circuit is indeed dead
BEFORE you do anything !

 

[Speedy Petey]

I actually think it's kind of funny, and very ironic, that he left the power on because of many computers in the house......and then the main breaker tripped.
I guess that theory went out the window. :laughing:

 

[rrolleston]

I actually think it's kind of funny, and very ironic, that he left the power on because of many computers in the house......and then the main breaker tripped.
I guess that theory went out the window. :laughing:

:laughing:

 

[oh'mike]

I always suggest the customers unplug all computers if there is major (or even minor if a neutral bundle is involved) work being done---a power surge could cost the contractor a bunch----

 

[rossfingal]

Yeah -
Lived in an apartment -
Electrician was in to work on the electric for the other apartment -
Had a computer on -
Somebody had done "substantial", screwing with the electric -
Smoke pouring out of my computer -
Ahhh! - I love the smell of burnt, plastic in the morning!

"RF"

 

[oh'mike]

I knew a handy man once who was on the hook for all of the appliances in a kitchen ---he popped apart a neutral bundle in a ceiling box----the surge toasted everything on two kitchen circuits--

Put him out of business----

 

[rossfingal]

I knew a handy man once who was on the hook for all of the appliances in a kitchen ---he popped apart a neutral bundle in a ceiling box----the surge toasted everything on two kitchen circuits--

Put him out of business----

Ouch!
That's why we have "testers" and "eye-balls" -
Maybe, they should be used!
Ya think?!?

 

[k_buz]

I knew a handy man once who was on the hook for all of the appliances in a kitchen ---he popped apart a neutral bundle in a ceiling box----the surge toasted everything on two kitchen circuits--

Put him out of business----

Shouldn't have been in business without insurance.

 

[oh'mike]

Shouldn't have been in business without insurance.

And--Should not have been messing with electrical in someones house without knowledge----

Your own home is one thing---doing it for hire without training---priceless.

 

[gregzoll]

Just looked at old receptacle. Tab is broken. You saved my butt! I know this is a bad excuse, but panel was not labeled and many computers were on in the house (not my house)

So, you are saying that you were doing unlicensed work on someone else's place, is how I am taking it. You are lucky you did not burn the place down.

 

[BigJim]

Mike what is a neutral bundle? Would that be a bunch of commons tied together?

 

[oh'mike]

Exactly---this is where power surges originate when someone is working on a circuit ---

I'll let an electrician explain fully--in a nut shell---two circuits each on separate leg in the breaker box can share one neutral---without over loading that neutral because they are on a different phase.

this is called a multi wire branch circuit---ideally the breakers would be locked together like a 220 appliance breaker.

The trouble begins when working 'live'---if the circuits branch out of a box heading to different rooms ,for example, you will have three neutrals in that 'bundle'---

if you have a load on both circuits---say one to your computer room and one to your kitchen---

and you remove the neutral heading back to your breaker box---but leave the other two connected----you will have the return load 'crossing over' to the other circuit--

The lights will become super bright---and all your LED displays will fry ,along with your computer--and the sensitive electrical supplies to the appliances.

I'm not a licensed electrician----So I hope I put this in an understandable manner---Mike----

 

[electures]

When the neutral of a MWBC (multi-wire branch circuit ) is broken it creates a series circuit between the two circuits. Since voltage will drop in a series circuit, the amount of voltage across each load will depend upon what is on and the current draw of each load. Something as simple as turning on a light changes the entire circuit. Losing the neutral at the service can have catastrophic results throughout the entire house on anything that is 120V. 220V appliances such as water heaters and airconditioners will not be effected.

 

[frenchelectrican]

I will throw my part as well .,

Like any spilt single phase circuits which it is typical used in North Americian side.

One example is on one side of MWBC is portable heater which it is 1500 watt then on other side of MWBC is your TV or computer which they useally draw about 200 ish watts and the netural is carry the differnce between the two loads.

Now let say someone which not aware this is MWBC and loosen up the netural for some reason instead of normal parallel split phase circuit it become series due the 240 volts will work it way around without netural so it will foruce 240 volts thru the example as I posted the heater itself will surive very easy but not for the computer or tv due the voltage for computer or tv will spike up anywhere from 140 to 240 volts depending on how well it designed.

That one quick prime example is 120 volt light bulb suddenly get super bright and burn out or explode ( I have see it happend from time to time but not often ) same thing with tv or computer or any appalinces with electronic control can get fried by overvoltage.

It will be the same idea with whole house system if you see large number of bright or dimmed light that usally indecated that you have comperised netural so anything on 120 volts will either get damaged or survived depending on the layout of circuits.

Oh by the way this not only affect the single phase MWBC's but it will do the excat the same thing with three phase MWBC's as well.

Let me post one example

one of our members in here do have wonderfull diagram so therefore Merci to Stubbie.,

Here the other one this will really clear it up alot .,

Merci,
Marc

 

[BigJim]

Thanks Mike, terminology just different from north and south. I really never thought about loosing the ground like you and Electures explained could cause a spike but I can sure see how it could now. It just never dawned on me that the two circuits could be crossed over in that way. I learned something new today and very valuable at that. Thanks a bunch guys, I appreciate that.

Marc, I appreciate your explanation also.