site lighting breaker amps

[mjmike]

When dealing with site lighting, I have a situation with a rather smaller lighting load yet the distance is requiring a heavy conductor. The fixtures are at 208V 1-phase. If I were to fuse each fixture at the base, can the breaker be larger than 20A? Where in the code is this allowed? I don't want to do a 3-phase circuit if anybody was thinking that.

In addition, say the conductor is #6, this obviously won't work with a 20A CB due to lug size. So, with multiple site lighting circuits, a contactor would be used. from the fixtures to the contactor, this would be #6, but then from the contactor to the breaker, could this be #10 or #12? I know this short piece of conductor would see the voltage drop as well, but at some point, I would have to make the conductor small enough to fit under the breaker lug.

 

[petersonra]

I am not entirely sure what you are asking, but in general there is no code prescription that prohibits you from making a wire larger than needed for the required ampacity or for the rating of the OCPD. You will need to upsize the EGC if you make the circuit conductors larger.

The ampacity of the conductor cannot be less than required for the load, nor can the rating of the OCPD be larger than what will protect the conductor.

In fact if you wanted to IMO, you could feed the lights on a 20A CB with #12 on one leg and #6 on the other as long as you upsized the EGC.

If you put fuses at the light, the circuit is no longer a branch circuit but a feeder, and you have to follow the feeder circuit rules, which are a little different.

It is not all that hard to splice a short section of #12 to #6 to make the connections at the breaker.

 

[mjmike]

I am looking to increase the amperage of the circuit. Typically, lighting circuits are only 20A. If I fused each fixture at the base, could say a 50A circuit be ran to serve multiple fixtures?

I believe, per 210.23, a 30A circuit is allowed for heavy duty lampholders although what is a heavy duty lampholder... Would this be the largest allowed and do the fixtures still get fused at 20A.

 

[petersonra]

I am looking to increase the amperage of the circuit. Typically, lighting circuits are only 20A. If I fused each fixture at the base, could say a 50A circuit be ran to serve multiple fixtures?

I believe, per 210.23, a 30A circuit is allowed for heavy duty lampholders although what is a heavy duty lampholder... Would this be the largest allowed and do the fixtures still get fused at 20A.

In my opinion, if you were to do this, the 50A circuit is a feeder and the lamp is actually being fed by a 20A branch circuit (assuming the fuses at the lamp at 20A).

 

[kwired]

I am looking to increase the amperage of the circuit. Typically, lighting circuits are only 20A. If I fused each fixture at the base, could say a 50A circuit be ran to serve multiple fixtures?

I believe, per 210.23, a 30A circuit is allowed for heavy duty lampholders although what is a heavy duty lampholder... Would this be the largest allowed and do the fixtures still get fused at 20A.

NEC doesn't really define "heavy duty lampholder"

Closest thing I can find but is still pretty limited is:

410.103 Bases, Incandescent Lamps.
An incandescent lamp for general use on lighting branch circuits shall not be equipped with a medium base if rated over 300 watts, or with a mogul base if rated over 1500 watts. Special bases or other devices shall be used for over 1500 watts.

I think any mogul base would be considered heavy duty, and some but not all medium bases would be considered heavy duty.

I think any HID luminaire would generally be considered to qualify for "heavy duty lampholder".

If you are allowed to use 30 to 50 amp circuits you are not necessarily required to use "supplemental" overcurrent protection, but it is a design option, and you can make taps using smaller conductors from the main circuit to an individual luminaire.

A short piece of 12 AWG from a 20 amp breaker to a 6 AWG sized for voltage drop, is not going to contribute any significant voltage drop to the circuit.

 

[don_resqcapt19]

In my opinion, if you were to do this, the 50A circuit is a feeder and the lamp is actually being fed by a 20A branch circuit (assuming the fuses at the lamp at 20A).

I don't think you can call it a branch circuit unless the fusing device in the pole is listed for the protection of a branch circuit. Most of the fuses of the type that you find in a pole would not be so listed.

 

[petersonra]

I don't think you can call it a branch circuit unless the fusing device in the pole is listed for the protection of a branch circuit. Most of the fuses of the type that you find in a pole would not be so listed.

Branch Circuit. The circuit conductors between the final
overcurrent device protecting the circuit and the outlet(s).

So how could you put a 20A fuse out there on a 50A branch circuit at all than if you reduced the wire size?

 

[GoldDigger]

So how could you put a 20A fuse out there on a 50A branch circuit at all than if you reduced the wire size?

You could always attach a 20A fuse to wires of the 50A circuit to protect utilization equipment, but if the wiring immediately downstream of the fuse is not part of that equipment, I do not think that you would be allowed to reduce the size of that wire below what is allowed for 50A.
JMO.

 

[cadpoint]

I'm looking at a simple cutler-hammer stab in 20 Amp breaker. On the side of breaker it lists torque
up to 6-4 AWG.

 

[don_resqcapt19]

So how could you put a 20A fuse out there on a 50A branch circuit at all than if you reduced the wire size?

Only if the smaller wire was permitted by one of the tap rules.

 

[Smart $]

... I don't want to do a 3-phase circuit if anybody was thinking that....

Why not?


You can reduce load current on a conductor by up to 13.4% where individual loads are combined and balanced. Reducing load current can be looked at from another perspective as increasing the amperage of the circuit.


Compare how much load can be powered by one 20A 3? circuit vs. one 20A 1? circuit (three wires vs. two) @ 208V, 16A load: 5,760VA vs 3,326VA.


Now compare two 3? circuits (6 wires) to three 1? circuits (also 6 wires): 11,520VA vs. 9,978VA... an increase of 15.5% (the inverse of a 13.4% decrease).


PS: Voltage drop also changes by the same percentage (ratio) at the same load current value: 1.732:2

 

[kwired]

I'm looking at a simple cutler-hammer stab in 20 Amp breaker. On the side of breaker it lists torque
up to 6-4 AWG.

Many 30 amp or less "miniature" breakers only accept 8 AWG max. Maybe you found one that does accept 6 AWG.

 

[hurk27]

When dealing with site lighting, I have a situation with a rather smaller lighting load yet the distance is requiring a heavy conductor. The fixtures are at 208V 1-phase. If I were to fuse each fixture at the base, can the breaker be larger than 20A? Where in the code is this allowed? I don't want to do a 3-phase circuit if anybody was thinking that.

Not sure what kind of site lighting you have in mind but if you only need a 20 amp circuit but need to upsize your conductors for voltage drop, it always been allowed by using a short pigtail to splice a smaller conductor on to the larger wire to connect to a breaker, the impedance of this short length of smaller conductor would not affect the impedance of the longer run, as pointed out any time you upsize for voltage drop you must always upsize the EGC proportionally that you upsized the circuit conductors, in the case of 15 amp through 30 amp (15awg-10awg) since the EGC for these size circuits is always the same size as the current caring conductors you will end up with the same size EGC as the circuit conductors. see 250.122(B)

In addition, say the conductor is #6, this obviously won't work with a 20A CB due to lug size. So, with multiple site lighting circuits, a contactor would be used. from the fixtures to the contactor, this would be #6, but then from the contactor to the breaker, could this be #10 or #12? I know this short piece of conductor would see the voltage drop as well, but at some point, I would have to make the conductor small enough to fit under the breaker lug.

For site lighting like parking lot lighting it was always very common to use 40 and 50 amp circuits for HID type fixtures, and most always installed an in-line 250/600 volt rated fuse holder in the handhole at each pole if for nothing else but to keep a fault in the ballast from taking out the whole circuit and to make trouble shooting a little easier, 240.5(B)(2) will allow you to use a #12 awg wire up the pole from the base where the 40 or 50 amp circuit feeds, as long as the load(s) on that pole do not exceed the rating of the tap conductor, they also make what we call a "pin reducer" that you crimp or has a set screw that allows you to connect larger conductors to smaller terminals.

Most all mogul and medium bases rated 660 watts or more are considered heavy duty 210.21(A), all medium base HID type fixtures will have a heavy duty rated base as well as being rated for the 4kv pulse start type ballast.

Also installing a fuse on a branch circuit does not always change the branch circuit to a feeder, and as supplementary overcurrent protection it is not required to be readily accessible as a branch circuit OCPD is, this is why it is allowed to be in the handhole. 240.10

 

[hurk27]

You could always attach a 20A fuse to wires of the 50A circuit to protect utilization equipment, but if the wiring immediately downstream of the fuse is not part of that equipment, I do not think that you would be allowed to reduce the size of that wire below what is allowed for 50A.
JMO.

See 240.5(B)(2)?

 

[Smart $]

See 240.5(B)(2)?

That allows it, regardless of supplementary OCPD, provided a fixture wire type listed in Table 402.3 is used.

Otherwise 210.19(A)(4) Exception... also regardless of supplementary OCPD.

 

[GoldDigger]

That allows it, regardless of supplementary OCPD, provided a fixture wire type listed in Table 402.3 is used.

Yes, but the section allowing fixture wire taps off a higher ampacity set of OCPD-protected branch wires is still subject to the unqualified limitation stated in 402.5 [2011], namely:

No conductor shall be used under such conditions that its operating temperature exceeds the temperature specified in Table 402.3 for the type of insulation involved.

This brings the ambient temperature factor, among other things, into the determination of just what types of fixture wire qualify in any particular use case.
It also leaves some ambiguity about what you can do, short of using OCPD, to make sure this condition is satisfied.
The hope is that the nominal load at the other end of the fixture wire is adequate as a current limiter.

The use of fixture wire is also constrained by 402.10 [2011],

402.10 Uses Permitted. Fixture wires shall be permitted (1) for installation in luminaires and in similar equipment where enclosed or protected and not subject to bending or twisting in use, or (2) for connecting luminaires to the branch-circuit conductors supplying the luminaires.

This does seem to match the OP's case.

I also question just how far you could run fixture wires between the tap points and the luminaires, although the Code does not appear to care.

 

[Smart $]

...
The hope is that the nominal load at the other end of the fixture wire is adequate as a current limiter.

Agree, but with a higher degree of certainty than "hope". I take the "conditions" to be the extreme side(s) of nominal.

...

I also question just how far you could run fixture wires between the tap points and the luminaires, although the Code does not appear to care.

I also interpret as no limit on length for 12- and 14 AWG. Smaller is length limited, but then we are talking 20A circuits.

 

[kwired]

Agree, but with a higher degree of certainty than "hope". I take the "conditions" to be the extreme side(s) of nominal.



I also interpret as no limit on length for 12- and 14 AWG. Smaller is length limited, but then we are talking 20A circuits.

And the 12 and 14 AWG are also on circuits that should be limited to 50 amp overcurrent devices, and sized to be no less than the load, those sizes generally have no problem carrying enough current to operate a 50 amp overcurrent device when called upon to do so. But I guess if you had an unusually long tap (that seems to be allowed) you could have enough resistance to increase that trip time.