Grounding In Series

[DesertGuy]

Example:

4 lights each requiring 100w of power. Positive wire is sized by 100/13.5 = 7.4amps (8.00). Each light receives its dedicated power supply.

Question:

When running a ground wire in series (lt.1 > lt.2 > lt.3 > lt.4 > Grounding Location) What size ground should be used? Would a ground wire sized appropriately for 8 amps be good, or is it a ground wire sized for 8 x 4 (32)?

Is it correct to think... electricity is not "consumed" in the lighting circuit and it is only the resistance through the filament that results in the light production; therefore, the ground wire needs suffucient load sizing to account for all power sources?

[2088 bob]

the grd wire should be sized to carry the combined load of all the lights when operating together if this is a 32 amp load allthough with with it being close to 30 amps i would go with a 10 ga wire remember when you get bigger than 10 gauge getting conventional stakons becomes impossible

[rickosuave1987]

I have my lights wired in series, 4 100w lamps as well. I have the ground the same size as the power. Even if each had a dedicated supply I would wire it so that the ground is the same size as if the power was in series as well.

[rickosuave1987]

I guess I type too slow. Bob's got ya covered.

[Marc]

...Is it correct to think... electricity is not "consumed" in the lighting circuit and it is only the resistance through the filament that results in the light production; therefore, the ground wire needs suffucient load sizing to account for all power sources?

Uh, no. In any simple circuit the current flow is identical at all points, from the source to (and through) the load and also back to the source.

"Series" suggests that the loads are wired so that the positive of one leads to the negative of the next, and so on. Putting four identical 12V lamps in a series configuration would result in only 3V being seen by each....and not much light ...your lights are not in series.

The configuration which you are referring to, using one common ground wire which leads from ground to the negative side of the first lamp, then on to the second's negative side, and so on, with a separate wire between the supply and the positive side of each lamp, is still electrically "parallel" - albeit with a "bus" topology on the ground side and a "star" topology on the supply side.
The ground wire could be progressively smaller the further it was from ground, since it would be handling less current at each stop. In your case, the wire from ground to lt.4 would need to handle 32A, the one from lt.4 to lt.3 would need to handle 24A, the next would need to handle 16A and the last only 8A.
Likewise, if you were to use a common "bus" wire to feed the positive side of each lamp it could also be progressively smaller the further it is from the supply - but that would make it awkward to provide each lamp with its own fuse protection.

http://www.allaboutcircuits.com/vol_1/chpt_5/1.html
http://en.wikipedia.org/wiki/Series_and ... l_circuits

[2088 bob]

marc's answer is bang on, i knew what you were saying when you were talking about the grd in series

[MNAirHead]

Dumb question.. isn't parellel onto a grounding bus preferred?

[2088 bob]

Tim what is being discussed is going out too the lights with one heavy ground wire and then jumping between each light with smaller ground wires

personally i would run a dedicated ground out too each light the same size as the feed wire most big driving lights are mounted to roll cages any way you might as well use chassis as ground as most of these lights use their mtding studs as a grounding point anyway

[Ol'fogasaurus]

A qualified agreement. Being that I am working on a shortened pan DB, I do not trust the pan as a dependable ground. I do not know who did the welding on it and given some things that I have found, I trust it even less.

On a rail that is pro done or done by a cert welder, I agree the chassis should be good. But if I buy something someone else has done I do a lot of continuity checking before I trust it. I also ground the battery to the engine/transaxle before grounding to the chassis. My way of doing it based on my experience.

Back in the dark ages, when I was taking electrical shop, the Navy gave the highschool several sheets of AL. It was long enough ago that the AL was only a three letter disignation... as I remember. Anyway, one of the guys in radio shop built a radio with a piece of it, a very nice job of wiring too. When they plugged it in... nothing. After a lot of circuit testing they accidentally came up with the solution, the AL in the chassis would not conduct. The went down and tested the sheets of AL and found only a couple of spots in all the sheets where there was conductivity.

Since then, I do not trust anything without checking it out. Grounding problems are probably still the biggest problem that autos still have today.

My $0.25.

[MNAirHead]

So guys.. is it adviseable NOT to run series ground..

Wouldn't this create a mystery situation when ground is lost?

Isn't parellel ground through a bus considered the best option?

Looking to learn (while planning my ride).

Tim

[DesertGuy]

OK, my terminology leaves alot to be desired; however, I think the question was understood. I agree that for ease and simplicity, having a separate ground for each "light" circuit would be ideal. However, suppose that the lights are mounted in such a way that there is a rubber bushing between the rack and chassis, this would interupt the "chassis ground". What option(s) would be available to bypass having four positives and four negatives running from the rack... or is that the best solution?

I see your issue.. would be good to ground to the rack.. then ground the rack to the body or a wire.

[david58]

So guys.. is it adviseable NOT to run series ground..

Wouldn't this create a mystery situation when ground is lost?

Isn't parellel ground through a bus considered the best option?

Looking to learn (while planning my ride).

Tim

I just rewired a motorhome. At the battery it looked like a nitemare, there were about 6 pos and 6 neg wires hooked to the batttery cables. I installed 2 bus bars one for each, and ran a battery cable to each. The frame should carry a ground anywhere if it is properly grounded. Meaning it isn't a rusted crusty. So to answer that question it is more a personal preference on how to run the ground wires. Manufactors use the frame, engine, tranny and body instead of running separte grounds.

[Ol'fogasaurus]

I can buy that answer.

A chassis ground is a convenient ground plane. Chassis gorounding is OK as long as you check things out before you rely on it (the same for any thing I guess). Don't assume! Always chase the threads if you use a bolt or a post for a chassis ground. I also clean away any paint, rust, crud, etc. before I connect the ground wire. I also check the location I am going to use to make sure that, electrically, there is conductvity at that grounding point.

Individual wired grounds are OK also as long as they follow the normally accepted rules. Bussing a is good, (especially with the right person - sorry - I couldn't resist) as well as is "daisy chaining" the buss of the terminal block. You just need to have a ground plane that is compatable with the positive wiring and it (easily) checkable/verifyable.

[MNAirHead]

Thank you..

I have a rail that will be doing a thread on shortly (mine).. I have found locations that the welding ground will not send to.. it was tigged by one of the bigger well known expensive factories.