B2710 Lights

gordon · Jul 18, 2000

So please tell me George what would the proper design voltage be 11-12-13-or14 volts. Should we go for the low watts or the high amps in order for the circiut to work. How much of a pad should there be as to wire size versus ampload at a given voltage?
Gordon

TomG · Jul 19, 2000

I'll try to keep my intellectual interest from bulldozing my practical interest. I didn't think that the state of the battery or alternator is going to create any significant surges-not practical, just interesting.

From what I remember, the battery should be a parallel load on the alternator. A discharged batter would show as reduced resistance for that leg which would be reflected in the voltage drop across the entire load. The higher alternator current drawn to charge the battery also would increase the voltage drop across anything in series with the entire load. For example, the ground cable and connections. Practically, probably not much of an effect on marginally high lighting loads, but it does make a good case for periodically cleaning battery posts and ground cable connections. Wonder if I remember all this correctly?

Good point about slow blow fuses. They don't take long to blow in an over-amperage condition, but the wire would heat somewhat during that period. I don't suspect it would make much difference in residential circuits where ordinary circuits are de-rated to 75% of the wire's capacity. I don't know if automotive circuits are similarly de-rated. By the same token, in Ontario, residential lighting and baseboard heating are considered fixed loads and can be loaded at 125% of the wire capacity (I think no wire bundling is allowed). By a published interpretation of the Ontario code, 3600 and some watts of baseboard heating can be wired with 14-gague wire and using a 20a breaker. My inspector is checking that with his technical people right now. I think that 2700 watts is the 125% over-rating typically allowed for fixed loads. I have a circuit with 2700 watts & 14-gauge wire.

If a tractor's circuits are similarly de-rated, then conceivably a 12a fuse could be installed safely if the load was only lighting. That, of course, would take an engineering assessment and agreement from the warranty folks. Anyway, it's interesting more than practical. Myself, I avoided these issues by running heavy unbundled wire from the battery and using an appropriate in-line fuse. I think that the comment about heat dissipation and bulb sockets is a practical thing that should be considered.

W5FL · Jul 19, 2000

Tom,

In the US, we are required to design to the National Electric Code. I know what you are trying to say, but codes sometimes allow you to place a combined load greater than the breaker (such as a lighting load) assuming that you won't have every light and appliance on at the same time, but NEVER to use a conductor at 125% of its rating.

Slow Blow fuses cause fires under many short circuit conditions, particularly in residential applications and they are ONLY used for inductive or high surge loads.

In the US if you use a 20A breaker and #14 wire you FAIL the inspection and you would be very UNWISE to allow that in your home. Wire is cheap, use 12 gauge for all 20A circuits.

Don't change FUSE SIZES in tractors. Wire another circuit if you can't live within the proper ratings. The heat increase 44% in the 12A vs 10 fuse example you use and that is unsatisfactory. You did the right thing making another circuit.

Maybe they will let you guys use SNOW covered wiring harnesses in the cold country, then all bets are off. /w3tcompact/icons/laugh.gif

TomG · Jul 21, 2000

Yes, I'd never put a larger than speced fuse in a tractor circuit without manufacturer approval (which would require an engineering assessment). My point is that lighting is considered a fixed load, but there is some surge at start up. If a fuse habitually blew at start up, then a slow blow or larger fuse could remedy that condition. The idea is possible since conductors often are required to be de-rated to accommodate things like surges. The idea is possible, but I guess I should have added emphatically; 'only with manufacturer approval.'

The baseboard circuit (2700 watts on 14-gauge wire and a 20a breaker) is inspected and approved. I wired it with 14-gauge because quite a bit of it had to be BX wire, and I already had the 14-gauge BX. I don't do wiring that isn't inspected and approved, and don't think anybody else should either. There may be some differences between U.S. and Canadian codes, but I thought they were very similar.

I guess I have an unusual attitude. I consider electrical inspections as one of the last genuine public services provided by government (That is, a service at a high quality and a realistic price). Of course, our electrical inspections were privatized several years back. The fees went up a bit, but the service quality is still good. To me, permit and inspection fees still are a lot cheaper than contractor rates. Contractors have the object of making money, but the interests of homeowners and inspectors are much the same: It's good if people don't get electrocuted and houses don't burn down.