So I need to turn the breaker off when I change a 3-way for a light?
Inlet on boiler
- Thread starter M. D.
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So I need to turn the breaker off when I change a 3-way for a light?
- Location
- Massachusetts
Nope, not one milliamp.
Lets say you have a 9 volt battery as a power source, now you hook up a conductor from one pole of that battery to the neutral in a panel.
Will any current flow in the single conductor?
I would say the majority of 'real' transfer switches do not switch the neutral. In some commercial applications the neutral will be switched for reasons not related to utility personal safety.
- Location
- Massachusetts
I guess so if in fact the 3 way has two live sources present.
I think OSHA might actually require LOTO for Edison base lamps, the sockets are not finger safe.
cadpoint
Senior Member
- Location
- Durham, NC
- Occupation
- Electrician - but not by NC Law.
Originally Posted by jim dungar
The last time I checked with Hubbell, their answer was that a three-way switch is not rated to transfer between sources of power. It works fine for transferring loads, but it lacks the internal clearances/insulation required for live source to live source switching.
Come on, complete your reading
, Well, OK thats where I went. All devices shall be rated for there service, ETC... , is my continuing thought here.
LLSolutions
Senior Member
- Location
- Long Island, NY
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
If all you have is one single pole breaker feeding the switch then you only have one live source.
steelersman
Senior Member
- Location
- Lake Ridge, VA
don't you mean DPST? That way you flip one switch and both poles are switched. That would seem better IMO.
A DPST would only be capable of controlling one power source. A DPDT is like two 3-ways mechanically connected.
steelersman
Senior Member
- Location
- Lake Ridge, VA
I don't think a 3 way is a SPDT since it is a single throw (ST) you are only throwing or flipping 1 switch. And as for the pole (s) I'm not sure if you should be able to say SP cause a single pole single throw switch would be an on/off switch, and a DPST would have 4 terminals not 3 like a 3 way has. Maybe a 3 way is technically a APST (alternate pole single throw).
- Location
- Massachusetts
I agree.
A DPST (Double Pole, Single Throw) switch has only "ON OFF" positions.
A DPDT (Double Pole, Double Throw) switch has has "ON ON" or "ON OFF ON" positions
A 3-way has one common terminal. That's the Single Pole. It has two traveller terminals. Those are the 2 (Double)Throws. SP+DT = SPDT.
SPDT:
DPST:
DPDT:
Last edited:
- Location
- Massachusetts
A standard three way is in fact a SPST.
The '1 switch' is being thrown between two contacts.
A normal single pole switch is a SPST, one switch being thrown against only one contact.
steelersman
Senior Member
- Location
- Lake Ridge, VA
meaning the # of toggles is the # of throws. since a 3 way has 1 toggle it is a single throw.Huh?
SPST = Single Pole switch?
SPST = 3-way switch?
If you mean 'Throws' = 'Toggle', a 3-way has two : Common to A, Common to B. Two=Double.
steelersman
Senior Member
- Location
- Lake Ridge, VA
it's a single toggle and it can only be changed one time, just like an on/off single pole switch can only go one change or one position change in one motion. Let's say it were a HOA switch, I can see your point there as there is only one toggle switch but you could change the switch to 2 different selections.
steelersman
Senior Member
- Location
- Lake Ridge, VA
It's still a single throw. YOur either throwing it to A or B.
- Location
- Massachusetts
steelersman
Senior Member
- Location
- Lake Ridge, VA
this last picture you posted could also be a single throw. DPST if there was one toggle switch changing both poles at the same time.A 3-way has one common terminal. That's the Single Pole. It has two traveller terminals. Those are the 2 (Double)Throws. SP+DT = SPDT.
SPDT:
DPST:
DPDT:
steelersman
Senior Member
- Location
- Lake Ridge, VA
ok so you contradicted what you said when you said a common 3 way is a single pole single throw. This first diagram shows a common 3 way being calld a single pole double throw. And I also stand corrected.Nope.
Here is an example of a SPDT switch
Here is a SPST switch
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