Jump to content
Electronics-Lab.com Community

120V shorted out, why did the lights get brighter?


Recommended Posts

I must have been tired and wasn't thinking at the time but I thought I'd try to make the GFCI that I had plugged into the wall trip by shorting out the connections. I know it was dumb and quite dangerous but I have one big question that came to mind, when it was shorted out the lights went brighter. According to the theory that I have learned, the lights should have gotten dimmer because the voltage should have gone close to zero and the amperage should have reached the maximum level at the shorted point. I am just curious as to why and how the lights became brighter instead of dimmer and also why the circuit breaker didn't trip.

Link to comment
Share on other sites

That's actually the only thing I could think of. Do you think it could also be the result of faulty wiring or bad components in the household wiring? My Grandpa did the wiring about 20 or 30 years ago and there are a lot of fluky things that he did such as having two items like a plug and light switch wired to two different circuit breakers. Also maybe it could be the result of aging circuitry? This whole thing has pretty much stumped me.

Link to comment
Share on other sites

Likely, you have less than good neutral connection at the service entrance box or the utilitie's transformer. In the US the service supply is from a 220vac center-tapped transformer. Half the circuits in a house are supplied 120VAC from neutral to one end of the transformer's secondary, and the other half are supplied 120VAC from neutral to the second end. If the  house neutral to transformer's center tap is lifted, the devices on the two circuits appear in series and become a voltage divider. If both circuits are equally loaded, each will see 120V.  But if not, the circuit with the lowest resistance devices (more heavily loaded) drops proportionally less of the 220V across its devices. The circuit with a higher resistance (less heavily loaded) drops more. So, when you short out one circuit, most or all of the 220V appears across the other circuit. The bulbs on the other circuit see a supply voltage much greater than 120V, get brighter, and then burn out. I saw this in my parents house.


Link to comment
Share on other sites

I checked the voltage in a few of the outlets in the house. Some were at 118 V and others (including the outlet that was shorted out) were at 125V. Could this be an indicator that the loads are not balanced in the service box and could that have influenced the thing with the lights?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...