Dangers of Multiwire Circuits 28.6
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- Опубликовано: 5 фев 2025
- “Multiwire” branch-circuits are advantageous in that they save money! But multiwire branch-circuits also present some unique hazards if not installed properly.
Find out what you need to know about the dangers inherent with multiwire branch-circuits by watching the video where Mike and the team discuss the theory behind these circuits.
This video is extracted from Mike Holt's Understanding Electrical Theory Library www.mikeholt.c.... For additional information call 888.632.2633.
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![Branch Circuit, Multiwire, NEC 2020 - [210.4], (19min:38sec)](http://i.ytimg.com/vi/Qynp92rIlYg/mqdefault.jpg)
I'm thankful I learned these lessons early in my career. Not everyone does, and, unfortunately, this is why we have code changes that tend to bring everyone down to the lowest common denominator in skill set, while raising the cost of electrical installs in the process.
I enjoy mikes law, The most expensive piece of equipment will sacrifice itself to save the least costly.
Fun story. When I was growing up, the voltage used to drop rather low. We could tell because the picture in our (CRT B&W) TV would shrink horizontally. The TV repairman said it was due to low voltage. We called the utility and when they came out, they said that *every circuit* in the house was on *THE SAME BUS* of our 120/240 service! An electrician came out and remedied that.
Maybe the panel was wired just before quitting time on a Friday … 😀
The infamous brown neutral.
Ran across a few of those and THAT is just one of the many examples of why the code updates are so important.
Thanks for sharing, Mike and Co.
Great information Gentlemen
I’ve seen overloaded neutrals many times due to what they talked about…. A 3 wire cable with both circuits on the same phase due to installing on a tandem breaker. I’ve also seen lots of expensive equipment burnt out due to losing the shared neutral when the circuit was wired on a proper 2 pole breaker so each wire is on their own phase. This stuff happens a lot.
I've seen this a couple different times where the main neutral at the electrical panel or meter socket became so corroded at the termination point that it drops connection. Equipment burns up real quick.
Mike only brushed over the fact it could be the utility company/service. I have been to several calls where the problem was at the top of a service periscope, weather-damaged, and also at the back of the service entrance behind the meter. (It's odd watching the dishwasher come on and other items in the house dim or stop working., then the dishwasher stops and everything else becomes brilliant.
This is the only video I found that explained why some things fried when I disconnected a neutral wire. The home apparently has more hots than neutrals.
😊
Thank you Mr. Holt. I will add E^2 over RP to my P over IE, and E over IR memorized formulas. I think of all the times I have taken the long way around.
Anytime you install a tandem to create more space. You have to payatention to what your doing.
We didn't loose a neutral but lost a phase to out factory. The voltage to one of our furnaces was low enough that the heater contactors could not pull in but the voltage was still high enough that it burnt up the coils in the contactors because of the high current from not pulling in.
Good topic, I enjoyed the panel of “Toppers” LOL
Good news is many new devices can run between 120 and 240 with no change. Today’s computers support dual voltage for the most part as well. Probably has a lot to do with global market.
I remember an amatuer home developer accused me of doing something like this because her furnace wasnt working.
Turned out the thermostat was just off.
Her so called furnace guy told her I fried it before even checking the thermostat. You cant make this stuff up.
Had a boss who opened a neutral in a 3phase panel in a kinkos copy store and fried 2 blueprint copiers.
😮
Does anyone know Mario’s Instagram or info ? I would like to follow him he gave some great information!
Mario is part of Mike Holt Enterprises and his personal Instagram account does not have anything electrically technical. His account is 'Mario.Valdes_'
Your illustration showing the "Correct Way" of wiring of 2 branch circuits is also incorrect Mike. The way I've always done it is to use an individual neutral paired with a "hot" all the way from the respective panel for every branch circuit. (Your illustration seems to show a shared neutral for the 2 branch circuits)
Lol... a multiwire branch circuit is permitted by the NEC, so it's not incorrect. If my video is about a multiwire branch circuit, then I need to show the multiwire circuit. Not two separate 120V circuits. Hope this helps...
I still refer to them as Edison circuits... showing my age.
Edison did use 3 wire DC distribution. Back when they wee debating AC vs DC, Edison's 3 wire DC could easily be switched to split phase AC without modifications. Edison had a lot of installed lighting systems and many, many of his 110 volt DC bulbs in service. The bulbs worked fine with either AC or DC.
Technically, Edison lost the war of the currents, but he still made a lot of money selling his light bulbs. In the long run, AC was better for distribution and 110 volts was safer than 220 volts. It worked out quite well and was a more efficient way to distribute power.