George, he knows this well, he said phase in double quotes for that reason. I agree, however, inspectors should know the difference and it’s best to refer to them as leg A and B to prevent confusion.
2 Likes
Exactly the reason I used the quotes. I knew that you would be smart enough to understand.
1 Like
Thanks for the info. This clears things up for me. I think it mainly goes back to me incorrectly thinking it was using both legs of power, which, in turn, goes back to my misunderstanding of how this bus was organized. Your explanation does make it all make sense though.
1 Like
I think I am following along, gents. I just want to confirm what I think I am seeing on the panel. A double-throw breaker has a Black and Red wire. The Black wire is going to a load somewhere,and the red wire is going to yet another breaker, on the same bus. The reason this is, so as not to risk overload the neutral on the double-throw breaker at the top. Correct? Theo Critch
That’s correct. Since this is a 3-wire MWBC the two 120 volt circuits cannot terminate on the same bus stab (the metal square).
2 Likes
George, You’re The Best!
From what I understand of single phase lighting circuit, or equipment circuit for that matter.
A single phase power is a two wire conductor, ac - alternating current power circuit. Typically/usually/normally there is one power wire/conductor, or the ‘phase wire’, and one neutral wire, the return, with current flowing between the power wire, the load, and the neutral wire.
A 1Ø circuit could also be 240 volts without a neutral conductor.
I’ve been a master electrician for a long time and I’ve never heard of a double-throw breaker. I seriously doubt that such a thing exists.
Robert,
Single phase means there is a single secondary coil or multiple coils in series. Single phase does not require a neutral. Different Voltages can be obtained by placing taps anywhere along the coil between the two ends.
In residential electrical systems, there is a tap midpoint on the secondary coil. That’s how we get 120V from a 240V secondary. That conductor is also solidly grounded and is called either the Grounded Conductor or Neutral Conductor. The nominal Voltages in the US are 7200V on the primary and 240V on the secondary.
Regardless of the number of taps, single phase is always single phase. You will often hear home inspectors and (sadly) some electricians refer to “opposite phases” or say other things that imply that there is more than a single phase. They are just wrong.
Likewise, you will often hear home inspectors refer to Floating Neutral. Neutrals in a residential electrical system are NEVER floating. They are ALWAYS solidly grounded.
Also, an electrical system can have any number of phases. In the US, we had one, two, and three phase systems but two phase systems never really caught on. There are very few, if any, of them in existence.
1 Like
Putting misinformation in quotation marks doesn’t make it right and it is misleading to those who are trying to learn.
One of my biggest challenges as a trainer is getting new inspectors to understand that they cannot rely upon forums for accurate information regarding electrical systems. They come to me with all sorts of misconceptions because of stuff they have seen on forums. The problem is compounded when they got the misinformation from someone who claims to be an electrician.
Nearly all who come to me with no electrical background mistakenly believe that there are two phases in a residential electrical system.
Yes, you have, by its more appropriate name: a double-pole breaker 
BTW, it’s a good thing you keep us on our toes, Mr George!
2 Likes
The most common double-throw device in residential wiring is a Three-Way switch. It is Single-Pole, Double-Throw. Double-throw devices can have one or many poles.
Double-throw switches, contractors, and motor starters are all very common in commercial and industrial wiring. An example is a motor with dynamic breaking. In one position it supplies electricity to the motor. In the other position, it directs the electricity being generated by the motor, after it has been de-energized, into the braking resistor so the motor’s magnetic field can collapse more rapidly and allow the motor to stop more quickly.
Other examples include things like lighting contactors that energize luminaires from an alternative power source on a loss of electricity and Automatic Transfer Switches.
Evening, George. Hope this post finds you well.
I said, From what I understand, Typically/usually/normally there is one power wire/conductor, or the ‘phase wire’, and one neutral wire. I do not think I referred to the return as part of the phase. I was referring the neutral as the power return.
Morning, George.
Again, I hope this post finds you well.
When I hear someone on the MB refer to a ‘float neutral’, the reference is to a remote/sub panel. The reference floating referring to, the neutral bus/busses are not in contact with the a metal panel enclosure due to the fact the equipment ‘should be bonded.’
PS: I will PM you.
I have a friend that purchased a condo. They can not sleep due to the HUM.
Bathroom directly under the buildings’ power transformer.
I have all the physical distance measurements to walls and ceiling.
The transformer faces the main fire escape and next to an elevator shaft directly above their bathroom.
< 5’ in front and to the right ><3’ of the transformer are 4 X 4" vertical cast iron sanitary pipes.
SIEMENS CAT: T3G30225A5VXX Distance Mod. CDTA0225VHA6XXBA
DRY-TYPE TRANSFORMER
Robert,
I’m sorry if I didn’t explain myself well. The two leads from the transformer’s secondary are the ungrounded (aka Hot) leads. Each has a potential of 240V RMS with reference to the opposite leg. At any given instant the actual Voltage on one leg is between -339.6V and +339.6V (nominal, as measured with an oscilloscope). At any given instant one leg is positive, Zero, or negative. When one leg is positive, the other leg is negative. In other words, the return leg is alternating. In the US, this cycle is completed 60 times a every second. The Voltage is Zero 120 times every second.
Meters used by electricians and home inspectors only measure RMS (aka Effective) Voltage, not actual Voltage. Actual Voltage is measured with an oscilloscope.
I have explained these concepts in more detail in the Home and Commercial Inspectors Electrical Group on Facebook. If you still do not understand, you know you can call me any time. If calling the US would cause to to incur international phone charges, send me a text message and I’ll call you.
1 Like
Yes. That is because they don’t understand electrical systems. When misinformation is repeated often enough, people will begin to believe it. I can’t stress enough that neutrals in residential electrical systems 𝗡𝗘𝗩𝗘𝗥 𝗙𝗟𝗢𝗔𝗧.
Neutrals are ALWAYS solidly grounded. There are no exceptions.
In other types of systems, neutrals are usually solidly grounded but in rare instances may be floating. They can also be resistance grounded but those aren’t very common either.
The important thing to remember is that if someone refers to a floating neutral in a home they are indisputably, unequivocally, wrong. I don’t care what rationale they try to use or how many times or places that they heard it from, they are wrong!
Dry type transformers can be loud. They vibrate and the vibration will transmit through metal and concrete. The best thing to do is to put isolation pads under the transformer to minimize the vibration transmitting through the floor.
George, I get the point but never ever heard someone refer to the neutral floating. The neutral busses are isolated from grounds in sub panels.
Neutrals should never be allowed to float . That always causes problems down the road. The only weirdity of a subpanel is that the grounds are a separate bus (apart from the neutrals ) and that is independently connected to the main panel’s ground / neutral bus
No George. Should be, but not always.
I’ve done many hundreds of service calls, electrical fire investigations, electrocution investigations, and almost any kind of electrical system failure that you can think of. All that is in addition to designing and installing electrical systems. In all my experience I cannot recall ever encountering a floating neutral in a residential electrical system. They are 𝗔𝗟𝗪𝗔𝗬𝗦 solidly grounded. No utility company in the USA will install or connect to a residential system with a floating neutral. In the extraordinarily unlikely event that the neutral were not solidly grounded at the house, it will still be solidly grounded on the utility company’s side.
In the very early days, decades before any of us were alive, systems were not grounded. It was soon discovered that ungrounded systems were unstable and susceptible to damage. Neutrals have been solidly grounded for more than 100 years. I seriously doubt that you or anyone else in this forum has ever or will ever see a floating neutral in a residence.
Just to clarify, neutral in a circuit disconnected, not the SEC natural.
1 Like