Coastalguy1
Member
- Location
- Virginia Beach, VA
I have a 26amp 120v lighting load which I want to control with a single pole switch. What size contactor do I supply and what breaker size?
thanks
thanks
help on lighting contactor circuit
- Thread starter Coastalguy1
- Start date
- Status
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
26/.8 = 32.5A, so you need a circuit rated 35A minimum and a 35 or 40A breaker, so thereby a contactor rated to that circuit size.
kwired
Electron manager
- Location
- NE Nebraska
I agree with the 35 amp conductor and breaker - unless this for some reason is not a continuous load - lighting generally is though.
I don't think the contactor needs rated 35 amps as long as it is not rated less than the load it is connected to. Keep in mind the contactor likely has a resistive load rating as well as an inductive load rating.
raberding
Senior Member
- Location
- Dayton, OH
- Occupation
- Consulting Engineer
lighting control
lighting control
or maybe two 20amp circuits thru a 2p contactor ???
lighting control
or maybe two 20amp circuits thru a 2p contactor ???
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yes, but keep in mind that the contactor has to be protected by the upstream device. If he ends up using a 40A breaker and the contactor is only rated 30A, technically it's a problem for that contactor.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Or two circuits & two single pole switches and no contactor.
stevebea
Senior Member
- Location
- Southeastern PA
What kind of lighting fixtures are we talking. If its more than a 20 amp circuit it has to be heavy duty lampholders, article 210.23(B)
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I suspect he is using a double pole contactor
- Location
- Massachusetts
Do you have a code reference in mind for that, in general switching devices are only required to be rated for the load they are controlling.
15 amp light switch on a 20 amp circuit etc.
- Location
- Massachusetts
I did not get that impression.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
No code reference other than the "suitable for use" rule, but I was just shooting from the hip. Here are the specs for the Sq. D 8903 contactors.
http://static.schneider-electric.us/docs/Motor Control/Lighting Contactors/8903CT9701.pdf
There's a chart on page 12, lower left, showing the maximum CB size for each rating of contactor. Turns out on that specific one, a 30A contactor can be protected by a 40A breaker. But not a 50A, there is a limit.
- Location
- Massachusetts
Interesting that if I use fuses I am not limited.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
This is probably not totally true but I thought fuses had a faster response time than breakers???? Not sure why that would matter.
kwired
Electron manager
- Location
- NE Nebraska
Are you seeing something I'm not? The table above the one for breakers is for fuses. The 30 amp contactor says max 30 amp fuse.
PetrosA
Senior Member
- Location
- Lancaster, Pennsylvania
In the paragraph about current ratings, it states that "All Class 8903 lighting contactors are fully rated for tungsten, ballast and
resistance loads. This means that a contactor can be used to control a load up to its full nameplate rating. Derating of the contactor is not necessary, as is the standard practice with circuit breakers and fuses."
With breakers, you would have to install a breaker for a full 30A load which gets you to 40A. Regarding RK5 fuses the Cooper-Bussman website claims that, "The time-delay characteristics of these fuses typically allows them to be sized closer to the running ampacity of inductive loads to reduce cost and provide improved overcurrent protection."
So there must be something about their characteristic curves that allows a 30A RK5 fuse to protect a full 30A load for the purposes of these contactors.
resistance loads. This means that a contactor can be used to control a load up to its full nameplate rating. Derating of the contactor is not necessary, as is the standard practice with circuit breakers and fuses."
With breakers, you would have to install a breaker for a full 30A load which gets you to 40A. Regarding RK5 fuses the Cooper-Bussman website claims that, "The time-delay characteristics of these fuses typically allows them to be sized closer to the running ampacity of inductive loads to reduce cost and provide improved overcurrent protection."
So there must be something about their characteristic curves that allows a 30A RK5 fuse to protect a full 30A load for the purposes of these contactors.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Coastalguy1,
I apologize for taking this out into the weeds a little by getting too specific with examples. The point I was originally trying to make was just a procedural one;
- Size the conductors for the load (and voltage drop if any).
- Size the OCPD (Over Current Protective Device, i.e. breaker or fuses) for the conductors.
- Make sure that whatever other devices you may have in the circuit, i.e. contactors, are suitable for the use, including being protected by the OCPD you end up with.
Coastalguy1
Member
- Location
- Virginia Beach, VA
It is a double pole contactor. The reply's got me what I needed to verify. Thanks to all!
timm333
Senior Member
- Location
- Minneapolis, MN
- Occupation
- Electrical Design Engineer
I have a similar situation. We have a photocell of 2100W, which means 17.5A. Previously somebody put 20A breaker on this circuit, is it ok? Or do we really need a breaker which is less than 17.5A?
- Occupation
- Licensed Electrician
Your question is a little confusing. Putting a 17.5A load on a 15A breaker would not be a good idea but I don't think that is what you are asking.
timm333
Senior Member
- Location
- Minneapolis, MN
- Occupation
- Electrical Design Engineer
Our actual load on photocell is very small (about 2A.) 17.5A is the maximum current rating of the photocell, which means that the maximum load this photocell can handle is 17.5A.
Can we put a 20A breaker for this photocell circuit? Or should we use 15A breaker?
Can we put a 20A breaker for this photocell circuit? Or should we use 15A breaker?
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