30-50 amp HID lighting circuits

[thunder15j]

We have a customer that is asking us to provide branch/feeder circuits for approximately 70-75 KW of lighting load for an indoor grow facility in an existing building. Existing service main is 480 volt-3 phase 3 wire. Customer will provide luminaires (Cali special "m" grow operation with lights on for extended time periods - continuous duty). I am calling out for 277 volt ballasts on their 750/1000 watt HID (MH or HPS) fixtures. I would rather not get into the merits of one type of lighting over the other in this discussion; my customer is the expert.

I plan on generating a neutral on the existing system by installing either a 75/112.5 kva single transformer of auto zig - zagging 3 smaller xformers (3 x 10= 103.8kva as per acme electric).

I will then go to a 200 amp panelboard with a neutral bar; then to lighting contactor; then out to the grow rooms with 4 wire circuits. As per nec 20 14 table 210.24, 15 through 50 amp circuits may be used for 1000 watt HID fixtures, assuming that the mfg used heavy duty lampholders. (Watch for "Ch" import mfgs).

Please help me by commenting on the following:

1) Even though 50 amp conductors, #6 cu, could be used, I am reluctant to go that route. If we use 4 sq and 5 sq boxes, #6 could be unruly. Also, we could see a higher failure rate of connections of #6 to smaller tap wires. Disastrous if a neutral connection were to fail. I feel much more comfortable using #8-40 amp of #10-30 amp methods.

2) Using auto transformer zig zag connections to generate a neutral to get my 277 volts. More bang for the buck. Any chances of floating voltages? Seems like I read about some issues with zig-zags in a post. I cannot see going 120/208 because of the need for more circuits. Also, 208 circuits do not allow for multi-wire circuits.

3) At the ends of the runs and also where branches are made from the main runs, which tap rules would allow smaller wire usage for the smaller loads? It is tempting to hardwire fixtures. Table 210.21 (B)(2) gives direction if you go to cord-plug.

4) If we use 4 wire circuits for 3 277V circuits with a common neutral for feeding our grow lights, are 3 pole breakers required? That would make troubleshooting a shorted/faulted circuit quite challenging and also shut down a whole bunch of lights all at once.

Thank you!

 

[JFletcher]

Re #4, handle ties would work, tho any maintenance of the lights/resetting tripped circuits would require shutting off 3 banks of lights vs 1. As there is a 12hr off cycle, that may be acceptable to your customer.

Why not go 480V fixtures with smaller conductors? Eliminate the transformers. Fewer branch circuits. Also, how can you use #6 with continuous loads of 50A/circuit? 208V wye would allow MWBC, tho you'd need ~2.3 as many to run the same number of lights, and 480/208V xfmrs.

Cord and plug is more expensive than hardwire tho lights could be shut off one at a time for maintenance.

 

[kwired]

Re #4, handle ties would work, tho any maintenance of the lights/resetting tripped circuits would require shutting off 3 banks of lights vs 1. As there is a 12hr off cycle, that may be acceptable to your customer.

Why not go 480V fixtures with smaller conductors? Eliminate the transformers. Fewer branch circuits. Also, how can you use #6 with continuous loads of 50A/circuit? 208V wye would allow MWBC, tho you'd need ~2.3 as many to run the same number of lights, and 480/208V xfmrs.

Cord and plug is more expensive than hardwire tho lights could be shut off one at a time for maintenance.

I have to agree with most of what JFletcher said, why not just go with 480 volt ballasts from the start?

No autotransformer needed, no open neutrals to worry about, use of 3 pole breakers is most likely way to set it up, but not really all that different then needing 3 pole breakers or handle ties anyway.

You will feed same KVA on a 50 amp three phase circuit whether it is 277 volt or 480 volt luminaires anyway.

You also have one less conductor to pull (the neutral).

If you want to lessen troubleshooting issues when one ballast fails and takes out all three phases with either method....use some supplementary fuses to isolate either each individual luminaire or smaller groups of luminaires.

 

[thunder15j]

thunder15j

thunder15j

The fixture mounting height steered me away from using 480 volt feeds...seems as though there is a minimum mounting height that is higher than our 12 foot mounting height when using 480V...I am looking for something in 210...

I was thinking hardwiring fixtures, but was not 100% sure of any code issues..not that we haven't done it before..have seen hundreds hardwired..

 

[thunder15j]

using 480 volt circuits for HID

using 480 volt circuits for HID

NEC 2014 210.6 (D) 600 volts between conductors...I think because of my lower mounting height (12-14 ft.) I might have a code issue. I would love to interpret it differently...

On a separate note...Experienced an unpleasant experience relamping a 1000 watt HPS 480Volt floodlight @ 40+ feet.. when screwing in the ballast tester (which shorts out the secondary for amperage test) I made accidental contact between the side of the lamp tester (mogul base) and the reflector... wrecked my tester ! Very nasty voltage for lighting...especially troubleshooting

 

[Ingenieur]

480 is 277 to G 210.6 C applies, not D
no mntg ht restrictions?

 

[kwired]

NEC 2014 210.6 (D) 600 volts between conductors...I think because of my lower mounting height (12-14 ft.) I might have a code issue. I would love to interpret it differently...

On a separate note...Experienced an unpleasant experience relamping a 1000 watt HPS 480Volt floodlight @ 40+ feet.. when screwing in the ballast tester (which shorts out the secondary for amperage test) I made accidental contact between the side of the lamp tester (mogul base) and the reflector... wrecked my tester ! Very nasty voltage for lighting...especially troubleshooting

Section you mentioned would limit you to 277 volt luminaires in your application, guess you need to derive 277 volts somehow, though
next question is what is grounded? If the supply is corner grounded, then you can't ground the derived neutral, that would create a fault to the grounded phase conductor.

I don't think you can have the neutral floating either though. How do you protect the neutral conductors which is actually an ungrounded conductor if that is how it is done? They may be somewhat inherently protected from overload but there is no overcurrent protection if neutral would fault to the grounded phase, which you shouldn't have any overcurrent protection on unless it opens all other conductors of the circuit when it operates.

You wouldn't be able to use 277/480 rated breakers either, would have to be straight 480 volt breakers. If you are a Square D man, this makes you use I-Line panels instead of NF panels.

 

[thunder15j]

Utility supply

Utility supply

Utility pole mounted single transformer has only three wires on their secondary bushings...they do no have a connection going to the 4th bushing, which I assume would be the 277V neutral connection..

I get 277 volts to ground when I test L1,L2,L3 to ground...that voltage is probably generated by the metering current transformers..typical older P,G&E older connection...also tells me it is an ungrounded Y supply..they make you go 4 wire when the meter or other gear needs replacement..

Still hoping we could use 480V branch, but cannot get that from 210

 

[thunder15j]

480 is 277 to G 210.6 C applies, not D
no mntg ht restrictions?

By golly, 210.6 C does fit the bill for 480 volts with 277 to ground. But now I am concerned about no having an adequate equipment grounding system since the utility does not provide the 4th wire...will have to consult with my consulting guy...

If I did go go with the Y transformer, we will bond the neutral to ground..

 

[electrofelon]

A few thoughts from my experiences with this:

1. 480 ballasts will limit choices quite a bit. A lot to all of the ballasts growers like to use (in my experience) are not available in 480, so if you were wanting to go that route, confirm first.
2. 480 will get you into hard wiring or very expensive cord and plugs. Plug and play can be advantageous depending on the situation.
3. With 277, I dont see any need to go over 20 amp circuits. With MWBC's you can get 4 fixtures per leg, 12 per full boat. No big deal, just stick with #12.
4. I did a room with 100KW. They were 277, came with nema 7 twistlock.

 

[JFletcher]

A few thoughts from my experiences with this:

1. 480 ballasts will limit choices quite a bit. A lot to all of the ballasts growers like to use (in my experience) are not available in 480, so if you were wanting to go that route, confirm first.
2. 480 will get you into hard wiring or very expensive cord and plugs. Plug and play can be advantageous depending on the situation.
3. With 277, I dont see any need to go over 20 amp circuits. With MWBC's you can get 4 fixtures per leg, 12 per full boat. No big deal, just stick with #12.
4. I did a room with 100KW. They were 277, came with nema 7 twistlock.

True, especially #2. A 75kva 480D - 480Y/277V xfmr is less costly than buying 75-100 480V twistlock plugs (extra cost over 277V cord and plug lights) and receptacles, and paying extra for 480V ballasts/fixtures

I dont think 210.6(D) applies unless the 480V service is corner grounded, in which case a xfmr like mentioned above would be prudent so to not have to use full 480V rated panelboards/breakers.

3/4" EMT can be filled with 16 #12s or 4#6s, tho 9CCC (12 conductors total with 3 full boats, 13 if wire EGC is used) would be max with the former w/o derating affecting OCPD ampacity. Wouldn't the neutrals be counted as CCC as the loads are wholly non-linear, limiting one to two boats per conduit (and then using 1/2" EMT)?

eta: if there are a perfect balance of lights (load) on each phase, in the uncommon event that you lose the neutral of the MWBC feeding them, you shouldn't fry ballasts.

 

[kwired]

Talk to POCO, maybe they are willing to change that transformer if it is old. Maybe if there is a charge to change it, it might be less then supplying your own transformer.

 

[thunder15j]

Talk to POCO, maybe they are willing to change that transformer if it is old. Maybe if there is a charge to change it, it might be less then supplying your own

The transformer would work, but they would have to pull the 4th wire in the underground conduit. Then a neutral bar with a bonding jumper to a grounding bar would have to installed.

Last time I checked with our power comp., they requested a complete main switchboard changeout.

A great idea if POCO would work with us.

 

[kwired]

The transformer would work, but they would have to pull the 4th wire in the underground conduit. Then a neutral bar with a bonding jumper to a grounding bar would have to installed.

Last time I checked with our power comp., they requested a complete main switchboard changeout.

A great idea if POCO would work with us.

Still you need to consider cost differences between what they want and what you would spend installing a customer owned transformer, with some factoring in of losses from that transformer over the time it is used.

If you are deriving a neutral where there wasn't one, you need a neutral bar either way.

I don't think you confirmed whether there is a grounded phase conductor or if this is an ungrounded system? Worse yet if it is actually a grounded wye but they never brought the grounded conductor to the service equipment?

 

[thunder15j]

The latter from above post is more than likely the case...4 bushing on pot and only three are connected...

Also because of reported use of electronic ballasts, I will now probably go with 2 wire 240V circuits..using a 240 volt secondary 3 phase delta with no neutral to deal with..

Sent from my SM-G925V using Tapatalk

 

[electrofelon]

Also because of reported use of electronic ballasts, I will now probably go with 2 wire 240V circuits..using a 240 volt secondary 3 phase delta with no neutral to deal with..

I dont really see the non linearity of electronic ballasts changing anything significant. For your branch circuits, yes could only get 2 full boats per raceway if the neutral is a CCC, vs 3 if not, but two is still 24 lights. How many lights in a row? For the feeder an service, your other loads (including sizable AC I assume) should make the non-linear load less than a majority.

Also keep in mind 240 is a bummer because you can only get 3 lights per circuit (277 gets you 4). So 4 wires with 277 gets you 12 lights, with 240 4 wires gets you 6 lights. Only advantage to 240 lights would be super cheap receptacles if cord and plug connected (I used 277V duplex twistlocks and they were about $20 a piece. Straight blades are cheaper, but in my case, the ballasts came with factor twistlocks).

 

[kwired]

I dont really see the non linearity of electronic ballasts changing anything significant. For your branch circuits, yes could only get 2 full boats per raceway if the neutral is a CCC, vs 3 if not, but two is still 24 lights. How many lights in a row? For the feeder an service, your other loads (including sizable AC I assume) should make the non-linear load less than a majority.

Also keep in mind 240 is a bummer because you can only get 3 lights per circuit (277 gets you 4). So 4 wires with 277 gets you 12 lights, with 240 4 wires gets you 6 lights. Only advantage to 240 lights would be super cheap receptacles if cord and plug connected (I used 277V duplex twistlocks and they were about $20 a piece. Straight blades are cheaper, but in my case, the ballasts came with factor twistlocks).

I think maybe when he said no neutral to deal with he was maybe thinking about harmonic issues on the neutral.

 

[electrofelon]

I think maybe when he said no neutral to deal with he was maybe thinking about harmonic issues on the neutral.

I also don't see that as an issue with modern equipment, maybe unless he uses super cheap poorly designed crap.

 

[kwired]

I also don't see that as an issue with modern equipment, maybe unless he uses super cheap poorly designed crap.

If electronic ballasts, it is non linear load, and in his kind of application likely the majority of the load to the facility, harmonics would be additive on the neutral of a wye system.

Might not be so much an issue at the branch circuit level but maybe at the service and feeder levels.

 

[electrofelon]

If electronic ballasts, it is non linear load, and in his kind of application likely the majority of the load to the facility, harmonics would be additive on the neutral of a wye system.

Might not be so much an issue at the branch circuit level but maybe at the service and feeder levels.

the few times I have measured this, I only got 2-3 amps on a fully loaded 20 amp MWBC, Probably less neutral current than you typical install of a bunch of dissimilar unbalancable stuff.