Why does connecting neutral to casing work?

[fredsilva]

I have basic experience installing switches, dimmers, outlets in my home; I am not an electrician.

My brother recently had a light that was not working and asked me to take a look. I have a basic question about this:

When I connected the hot wire and neutral to the light fixture wiring: the light does not work. But if I touch neutral coming from lamp fixture to metal casing the light works.

Why does this happen, I thought it should be a closed circuit.

I checked for power on the switch and it was receiving 120v.

Checking the circuit from the hot and neutral wires in the light casing, it registers very low voltage, which tells me the neutral is not circulating appropriately.

My question though is, why does the metal casing keep the light on?

Thanks for your help

 

[fredsilva]

Is it because the casing is flowing the energy back through the ground wire?

 

[pc1966]

Probably yes, using the ground as a return path.

But using a ground for power return is a VERY BAD IDEA as if there is an open ground fault then any attached metalwork is then live and dangerous.

That sort of arrangement (combined neutral & ground/earth) is known as TN-C and here in the UK is prohibited from use within installations. It is allowed within the power supplier's system but they have multiple earthing arrangements and separate N & E when it comes in to the property. Even then it is the cause of a few accidents every year due to open fault on the combined N &E.

 

[fredsilva]

Probably yes, using the ground as a return path.

But using a ground for power return is a VERY BAD IDEA as if there is an open ground fault then any attached metalwork is then live and dangerous.

That sort of arrangement (combined neutral & ground/earth) is known as TN-C and here in the UK is prohibited from use within installations. It is allowed within the power supplier's system but they have multiple earthing arrangements and separate N & E when it comes in to the property. Even then it is the cause of a few accidents every year due to open fault on the combined N &EIor your explanation

 

[fredsilva]

Thank you for your help good sir, this answers my question.

 

[Megawatt]

I have basic experience installing switches, dimmers, outlets in my home; I am not an electrician.

My brother recently had a light that was not working and asked me to take a look. I have a basic question about this:

When I connected the hot wire and neutral to the light fixture wiring: the light does not work. But if I touch neutral coming from lamp fixture to metal casing the light works.

Why does this happen, I thought it should be a closed circuit.

I checked for power on the switch and it was receiving 120v.

Checking the circuit from the hot and neutral wires in the light casing, it registers very low voltage, which tells me the neutral is not circulating appropriately.

My question though is, why does the metal casing keep the light on?

Thanks for your help

 

[Ziggie]

Sounds like you have a broken neutral away from the equipment. Should never use earth as a “live “ .

 

[Marvo]

Yeah, the ground is performing the function that the neutral usually would if it weren't broken.

As mentioned above you've created a connection arrangement where getting a shock, even at other locations on the same circuit, is highly likely. Do not leave it connected this way... rather find the neutral fault.

 

[Ziggie]

Does light have a wall switch ?
Typically, there are two wiring scenarios in the U.K.

 

[Ziggie]

Let’s guess at the situation . You stated that you measured a voltage at 120v - so I guess that you are not in the U.K.
I have very little knowledge of other countries but let’s have a go.

quite often for a light in a shed the flow is from the main customer unit (or a spur) there are 3 wires which run to the switch. The switch may work one or more lights .

in the switch , the live wire is connected to the “in” and the live wire from the other side of the switch goes to the lamp. The neutral is not used in the switch box but is moved on to the lamp. The earth may be used to earth the backbox of the switch and then goes on to the earth of the lamp.

the switch might be more complex and may switch both the live and the neutral.
In this case both the live and neutral have separate connections on the switch .

if this is your setup then you would check :
1.The connection of the neutral from the lamp to the neutral from the switch.
2. The connection of the neutral (if any) in the switch
3 the neutral from the consumer unit (or the spur.

 

[Ziggie]

The second wiring used in the u.k. for a floors worth of lights.

the live and neutral and earth come to the lamp holder of the first lamp in the chain of lights. This in live is connected to a cable to the switch and to the next light holder.The return cable (quite often a different core colour - should have a red or brown sticky tape on each end) comes to a new connection at the lamp holder. This connector connects to the lamp .



The neutral comes to a different connector which connects to the lamp and connects to the next lamp.

The earth comes in and connects to the switch box and the next lamp holder.

typically, if you have a fault there are several lights not working and the fault is either in the first one not working or in the last one working .

If you can say which one of the cases you have, then it should be easy to advise.

the switch might be any one of a number of devices - switch, fused spur, isolator, rcd etc.