Solar Billboard Sign Grounding

[timm333]

We are installing a 12V solar billboard lighting system. As 12V is very low, so I understand that we don't need equipment grounding, and all we need is the grounding of the billboard structure. Is it correct?

 

[jaggedben]

I don't think this is correct. The 2011 code says equipment grounding is required 'regardless of voltage'. 690.43(A).

(You are not required to have system grounding, but that is different.)

 

[timm333]

Yes this makes sense. It looks that the grounding of PV system is very confusing because there are conflicts between installation instructions/industry practices, and NEC

Another question: The solar light fixture already has an exisitng battery inside the fixture. We are putting an extra battery (outside light fixture) in parallel to this exsting battery. Do we need to put fuse to protect the cable from extra battery to the exisitng battery?

 

[timm333]

The solar light fixtures and solar panels are made of aluminium metal. Can we use copper cable for equipment grounding of lights and solar panels, or should we use aluminium cable?

The equipment grounding will be DC grounding because PV panels produce DC current. Can we use the same DC grounding rod to ground the metal structure of the billboard as well?

Thanks for your help...

 

[WIMaster]

I would recommend tinned copper for its' corrosion resistance, the fact that it can be used in direct contact with soil and the fact that it doesn't look like gold that needs to go to the scrap yard for $$.

I would also use Al/Cu lugs.

 

[timm333]

The solar light fixture already has an exisitng battery inside the fixture. We are putting an extra battery (outside light fixture) in parallel to this exsting battery. Do we need to put fuse to protect the cable from extra battery to the exisitng battery?

 

[BillK-AZ]

It would be better if you used just one larger external battery. For best battery life the charging voltage should be temperature compensated based on battery temperature. This is generally a feature of the charge regulation and should be located next to the battery. Do everything you can to keep the battery cool, such as an insulated enclosure, painted white, and kept in shade (if possible). In hot Arizona the battery and controller are often placed in buried boxes. One city insisted on black battery boxes on the pole in direct sunshine, and the batteries are failing quickly.

If you end up with two batteries, separated by a cable that can be damaged, fuse both ends according to the cable ampacity.

 

[timm333]

Each of the 2 batteries is 12V 8AH, so total maximum current is 8+8=16A. So if we use a battery-cable which is rated more than 16A (for example # 10 AWG), then do we still need to put fuses on both side?

 

[BillK-AZ]

You are confusing battery capacity with possible fault current.

Your 12V, 8 ampere-hour battery can supply high current for a short period, long enough to burn #12 wire in the event of a short circuit. Or the battery can explode if shorted.

If this battery is powering the lights for all night, then your current to the light is only about 1 ampere or less. The wire ampacity tables do not go down to this current, but you would be safe using at least a #18 wire and 5-ampere fuses at each battery.

 

[timm333]

Thanks for the information ... I can put 5A fuse/breaker. I understand that the fuse/breaker will protect the cable on the secondary side of the fuse/breaker. But there will be a small length of cable (6-8 inches) that will be connected from battery to the primary side of the fuse/breaker. How to protect this length of cable?

 

[timm333]

Please see the attcahed wiring diagram. I think the fuse F2 will protect both existing and additional batteries, so extra fuse to protect the cable between exisitng battery and additional battery will not be required. please let me know comments.

 

[tom baker]

Make sure you use a DC rated fuse. I use Bussmans KLM.
The fuse needs to be able to interrupt a short circuit on the leads
Some CBs are listed for DC applications.
both batteries need to be the exact same type.

 

[BillK-AZ]

The wiring most at risk is the wiring between the two batteries, your F2 does not protect this. Both ends of this external wiring must be protected as either/both batteries can provide current to a fault in this external wiring.

Fuses are not generally used for the PV module as it is not a source of overcurrent. Most charge controllers do not allow any backfeed to the PV module, so a fuse is not needed there. Any fuse internal to the light fixture (F2) that is part of the manufacturer's wiring must remain as manufactured.

If both batteries are not in the same thermal environment (operate at the same temperature), expect short battery life.

Your diagram shows grounding of the PV negative, this is incorrect. If you are grounding the circuitry, do it at the battery negative. If you do not ground the circuitry, then you should use 2-pole circuit breakers where needed for overcurrent protection.

If you can, see Exhibit 690.5 of the NEC 2011 National Electric Code Handbook for a general diagram. The example does not fuse the inter-battery connections because they are in the same enclosure.

 

[timm333]

Thanks BillK-AZ, I have attached the revised sketch here with changes in Red color.

I got the idea of grounding the PV negative from figure 8 page 28 of the link: http://www.nmsu.edu/~tdi/pdf-resources/NEC.pdf). But if it is not correct, I can removeit.

I will remove the fuse F1 unless already provided by the manufacturer.

Both batteries are actually 2.3 AH (not 8 AH). Should the fuses (F3 and F4) be rated for the short circuit current of one battery only, or should they be rated for the combined short circuit current of both batteries?

 

[BillK-AZ]

If you have a conventional charge controller, then the PV- and Battery- (as well as any load-) are internally connected, so it makes little difference which you actually ground. John Wiles shows the grounding to indicate that one polarity is grounded, in many cases the actual grounding is provided the charge regulator or the inverter in larger systems.

The fuses (F# & F4) are to protect the wiring and are based on the ampacity of the wire, not on capacity of the battery.

I still maintain that you will be better served by using one larger battery. 12V 7AH batteries are relatively low cost, please consider a single battery.

 

[timm333]

The manufacturer has one small battery already built-in the light fixture, so we cannot put one large battery instead of two small ones.

I have a problem. I was thinking to put one fuse (F3) inside the light fixture and one fuse (F4) inside the additional battery enclosure. But I talked to the manufacturer and he says that NEC fuse requirements are for grid-tie applications only. He is saying that our system is enclosed (not exposed); and putting an extra fuse (F3) inside the light fixture will void the warranty.

Are the NEC fuse requirements only for grid tie applications?

 

[K8MHZ]

The manufacturer has one small battery already built-in the light fixture, so we cannot put one large battery instead of two small ones.

I have a problem. I was thinking to put one fuse (F3) inside the light fixture and one fuse (F4) inside the additional battery enclosure. But I talked to the manufacturer and he says that NEC fuse requirements are for grid-tie applications only. He is saying that our system is enclosed (not exposed); and putting an extra fuse (F3) inside the light fixture will void the warranty.

Are the NEC fuse requirements only for grid tie applications?

When you started talking about modifying stuff I immediately thought about a warranty violation.

I'm going to want to think that adding a battery in any manner will violate the warranty.

A larger battery will increase the load on the charger, which may be in excess of it's design parameters.

 

[timm333]

Actually the manufacturer recommended putting extra battery; so it should be ok to use extra battery. The reason we need extra battery is because we want to light the billboard sign for all night long during the long winter nights.

The manufacturer says that fuses F3 and F4 are not required; and that if I put fuse F3 in the light fixture, it will void the warranty. But if it is required by NEC, then we will have to put the fuse, no matter what the manufacturer is saying.

Because the two batteries are in different enclosures so fuses should be required on both ends of the cable that connects the two batteries together.

 

[timm333]

I can use tin platted lugs (something like WEEDLUG-6.7) to ground the rails. Do I also need to ground solar-panels? Or will solar-panels be automatically grounded when tied to the grounded rails?

 

[timm333]

A couple of more questions: will the steel structure of billboard be DC grounded or AC grounded? Also do we need to ground the metal surface of the LED light fixture?