Switches - Line and Load

SmittysRV · #1 09-20-2010, 05:20 PM

In Van's wiring harness instructions it talks about putting the 1/2" copper buss bar across the switches, connecting one post on each switch to the single copper bar. The copper bar provides the positive charge to each switch. Each switch has "Line" and "Load" stamped on it next to the posts. I can't see in the instructions where which one gets the copper bar attached to it. In the drawing, it looks like the "Load" terminal get the copper bar and the "Line" goes to the device being powered. Anyone know which is which?

Mike S · #2 09-20-2010, 05:55 PM

Quote:

Originally Posted by SmittysRV

I In the drawing, it looks like the "Load" terminal get the copper bar and the "Line" goes to the device being powered. Anyone know which is which?

Other way around.

Load is the device you are controlling.

aerhed · #3 09-20-2010, 05:56 PM

Sounds backwards. Bus should probably be line side (if it matters).
P.S. I love exposed busses, how bout you Dan?

dlloyd3 · #4 09-20-2010, 06:40 PM

Smitty,
You're right, Van's direction has the copper bus bar on the "load" terminal, the switched device on the line side. Yes, backwards from what was intended by the manufactuer. Two electrical engineers and a real smart guy I trust assured me in this case it makes no difference.

SmittysRV · #5 09-21-2010, 04:10 AM

Thanks Dave. From all the things I read on the internet and some friends who came over to the garage/hangar, the whole setup seems backward. But I think you're correct, the copper buss bar goes on the "load" terminal. Here's the drawing I went by, showing the switch with the "line" going out to power that lights, avionics, etc: (sorry for the fuzzy pic)

Snowflake · #6 09-21-2010, 12:02 PM

Since it's a DC switch it's not clear why it matters which way around it goes, and you may want to have different switches oriented different ways. Why does orientation matter?

JonJay · #7 09-21-2010, 12:09 PM

Quote:

Originally Posted by Snowflake

Since it's a DC switch it's not clear why it matters which way around it goes, and you may want to have different switches oriented different ways. Why does orientation matter?

As long as "up" is "on" (closed). I suspect the buss is put on that side for physical reasons, not electrical.

elippse · #8 09-21-2010, 09:16 PM

Understand that when you "daisy-chain" several switches to one feed wire, that any voltage drop on the feed wire will be felt by each switch and passed on to their loads; this is know as common-mode interference. So if you have one of the switches controlling a load that draws several amps, and especially if the load is a pulsating load such as strobe lights, the intermittent voltage drop on the feed wire will get passed to the other loads. So if you have a load that is sensitive to pulsating voltage, such as an intercom, radio, or music system, it's really best to feed each switch independently from the main buss. This is even more-so on the return (ground) side of the circuit. To never have mutual interference from one device to another, always use individual wires from the unit's return to a single-point return.

gordodavis · #9 09-22-2010, 07:34 AM

I guess I'm a little confussed, if you use a buss bar across all the switches, how do you get individual circuit protection? Would you put fuses or breakers between the switchs and the devices rather than putting it above the switches. I'm familar with using a buss to link your breakers but not for the switches.

apkp777 · #10 09-22-2010, 07:46 AM

I am not a fan of connecting the copper buss across breakers because of what Eclipse mentioned. I have never heard of anyone doing it for switches. I am not sure how that would work. Gordo is correct, you would have to put the breaker on the load side of the switch. That's not a good idea. It's early, maybe my brain is still asleep. Someone chime in if I am not correct on this.

For trouble shooting I like to have the ability to isolate circuits. When you buss things together it become more complicated (IMO).