| Author | Message | ||
| L James Jones Jr (Jamo)
Registered Member Username: Jamo Post Number: 96 Registered: 11-2007 Posted From: 74.79.238.160  Rating: N/A |
Hi All, I'm in the process of running the new 12v. I'm using the 12ga THHN for the runs from my converter to a multi switch panel over the driver's seat. Each switch is fused. So...I have run the ground from that panel to the (-) on the converter. Will that, as well as the single line be enough to power (12) multi bulb lights & (3) fans? My plan behind this switch panel was to install a terminal block to ground each loop back to that (and directly to the converer). Should I be doing a terminal block to distribute the (+) leads as well? Will I need heavier cable (or multiple runs of 12g) for the mains? The water pump & furnace will be run directly from the converter. Guess another grounding terminal block there as well? The PO had all grounds to the chassis at each fixture and none of them were working until yesterday. Yeehaaaa...My wife & I had a couple Utica Clubs (favorite local beer) under the freshly lit ceiling last night. Progress!! Now if she could get used to all the hanging temp ground wires, I'd be almost done. Thanks much... Jamo | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 974 Registered: 1-2003 Posted From: 67.142.130.23  Rating: N/A |
Whether or not the #12 will be sufficient depends on the total current draw you anticipate. "12 lights and 3 fans" is not enough information -- you need to look up the wattage for each item, total it up, and divide by 12 to get the amps. The other information you will need is the total length of wire from the converter to the panel, so you can figure the voltage drop once you have the current. There are a number of voltage drop calculators on the 'net; once you have total current and length, you can plug those numbers in and get the proper gauge for your main run. If you don't intend to run all 12 light and 3 fans simultaneously, you can figure the most you will run at once and use that figure instead, but, in this case, you should have a main fuse or breaker for the panel that reflects this lower value. -Sean http://OurOdyssey.BlogSpot.com | ||
| Rob Norgren (Robsedona)
Registered Member Username: Robsedona Post Number: 148 Registered: 11-2007 Posted From: 75.210.231.111  Rating: N/A |
I have been thinking of doing the same thing I seem to have to go back and redo the - under the ceiling from time to time because they lose connection so was think of running a big ground up to the center and welding A bus bar their and then to the front and rear so I have a place to tie in all grounds to solid ground :-) Think you have a great Idea :-) Rob | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1683 Registered: 10-2003 Posted From: 71.58.71.157  Rating: N/A |
I would go with single thhn #8,or even #6 then drop to #12 at the panel for each switch, so you don't have voltage drops later when you want to add other items. Sort of like a fuse panel in the house. Wire is relatively cheap.Make sure you have a good fuse setup at the inverter end of the wire incase of a short down the road. | ||
| John (John_t)
Registered Member Username: John_t Post Number: 3 Registered: 10-2009 Posted From: 66.244.97.31 Rating: N/A |
To begin with, a branch circuit should be fuzed at the source (the Converter) NOT somewhere way down the line like at the switches. Its the feed wires out of the converter that need protection so they cant draw excess current beyond their ampacity to the point they overheat and degrade the insulation. However, that dont mean one cant still go ahead and fuse at the switches output if he likes (no harm in more protection), but if theres no protection at the converter source the wires from it up to the switches input ARE NOT PROTECTED. However, many converters have fuzes for each output circuit so hopefully your fine and I just didnt interpret the question properly. Next as to sizing the return current path for multiple switches, the post above is absolutely correct, you need to know the total max current draw before that can be calculated. However that being said, Id venture a somewhat educated guess and Id go ahead and use at least an 8 gauge wire for that, which may or may not be overkill DEPENDS ON THE LOAD.......That 8 or even 6 gauge bigger ground wire could terminate at a master grounding multiple terminal block up near the switches. In cases where youre gonna be sleeping in these conversions (well DUH) one can never be too safe when it comes to BOTH the 120 VAC and 12 VDC wiring AND SO often in a 12 volt circuits ITS THE GROUND THAT CAUSES A PROBLEM, so be sure each branch circuit (out of converter) is properly fuzed at its source and if you wanna individually protect circuits out of switches to individual loads, all the better. Since these 12 VDC loads are primarily resistive (other then say a water pump) one needs regular (fast blow) single element fuses NOT any dual elelment time delay type often used for AC motor starting. Although Im new on these Bus forums since I tired to help my buddy fix his 4104 Spicer clutch problem, Ive been RV ing for almost 40 years and love it Best wishes n God Bless yall John T Long retired Electrical Engineer in Indiana | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 293 Registered: 12-2000 Posted From: 72.187.35.208  Rating: N/A |
I would not recommend THHN for low voltage wiring. It will work but I would suggest a finer stranded automotive wire. The THHN is a course strand and not as flexible as I would prefer. | ||
| John (John_t)
Registered Member Username: John_t Post Number: 4 Registered: 10-2009 Posted From: 66.244.97.31 Rating: N/A |
Len, cant you get fine stranded wire with THHN insulation same as you could get solid or coarser stranded wire??? I been away from the trade since my 1991 engineering retirement, but I thought THHN was strictly the class and type of INSULATION unrelated to what type or size of wire was enclosed therein, be it solid or fine stranded or heck even aluminum wire enclosed inside THHN "INSULATION"?????? Like I say I been retired as an engineer toooooo long and rusty as an old nail so my memory may well be wrongggggggggggg lol God Bless, John T | ||
| L James Jones Jr (Jamo)
Registered Member Username: Jamo Post Number: 97 Registered: 11-2007 Posted From: 74.79.238.160 Rating: N/A |
Thanks for all the info... I did plan on running from the fused terminals on the converter to the switch panel & other runs. I was just hoping to run a "main" up to that switch panel (and back with a ground) to make it easier to run my lighting circuit, a couple winshield fans, the stereo, the CB, maybe the GPS if I ever get one... To run this main & ground, can't I just run two lines (each) of THHN 12g for it? Another 2 lines back for the ground?? I have plenty of THHN 12g...guess I might as well tell the story. My wife & I went to Lowes to buy 100' of each...wh, blk, & gr. The price was way better (less $$ overall) to buy the stuff on 500' reels, which I did. Got to the cash register and this nice girl, of Bosnian decent, waited on me (broken English). She tried to charge me $145 per roll & I explained the full reel discount. She called a manager & he told her to push this and punch that, & the screen showed $45 per reel. I said "that's it, and I have 3 of them". She punched few more keys and the total price came up at $0.87...yeah, eighty seven cents...after tax!! I argued with her & said I owe her another $130 some bucks and she got beligerant with me. I looked at my wife, shrugged my shoulders, put my credit card away and gave her a buck. Waited for my change too. Hey, I tried, and I slept well that night too. So...I'm using 12g THHN for lots of stuff for a while. Thanks again Folks... Jamo | ||
| John (John_t)
Registered Member Username: John_t Post Number: 5 Registered: 10-2009 Posted From: 66.244.97.31 Rating: N/A |
You can use paralell conductors, of course two No 12 wires is twice the ampacity of only one. However, you need to protect that paralell wire combination with a bigger fuze if you intend to pull more amps through it, but on some of those converters they may only have like 20 amp max fuze blocks??? Sounds like youre wanting to run 40 amp wire capacity up to a terminal and tap 3 or 4 seperate fuzed branches off of it. So long as the main trunk circuit is protected with a 40 amp fuze and has 40 amps worth of copper that sounds okay, and then if each of the load branch circuits (fed from the main trunk) is protected with a fuze to match their individual ampacities that sounds okay, just remember the TOTAL of all the individual loads cant be greater then the main trunks ampacity. Im NOT so experienced in low voltage DC circuits, I was a secondary power distribution designer for single and three phase 120 to 480 volt AC circuits, SO NO WARRANTY ON ANYTHING I SAY........Sorry | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 976 Registered: 1-2003 Posted From: 67.142.130.18 Rating: N/A |
Actually two wires is not twice the ampacity of a single wire, because there is no way to guarantee that the current will split evenly between them. Differences in length, broken strands, and even variations in torque at the terminals will cause one wire to carry more current than the other. For this reason, when doubling wires for additional capacity, it is necessary to "de-rate" them by a certain percentage. Electricians follow a set of tables for how much to derate depending on circumstances. Absent any more complete information, 75% is the accepted safe figure. So let's say you look up the allowable maximum ampacity for the type of wire (27 amps for THHN #12 copper under 90°), then apply the appropriate de-rating for temperature, number of conductors in the raceway, etc, and then adjust for voltage drop on your length of run (which will be higher for DC than AC) and expected load, and find that the #12 is able to carry, say, 19 amps. Twice 19 is 38, but you need to apply the derating factor for paralleled conductors; 75% of 38 is 28.5 amps. The nearest fuse size below that is 25 amps, so that's what you should fuse your feed at for paralleled conductors. Again, this number is just an example -- you need to figure your run length and calculate the voltage drop for your specific installation. -Sean http://OurOdyssey.BlogSpot.com | ||
| John (John_t)
Registered Member Username: John_t Post Number: 6 Registered: 10-2009 Posted From: 66.244.97.31 Rating: N/A |
GREAT INFO, for sure in an "ideal" world the lengths and torques would be the exact same (our electricians did a great job when they made up paralell runs) and theres twice the copper and twice the ampacity BUT WHO CAN LIVE OR INSTALL WIRES IN SUCH A PERFECT SETTING HUH.... While he would like to use all that No 12 he has, I think he would be better off investing in some No 6 or 8 (not that expensive for say 60 total feet) wire and do it right BUT IM STILL AFRAID HIS CONVERTER is set up with a bunch of 20 amp terminations. As typical in these situations THERES NO FREE LUNCH but provided all his feeders and branch circuits are properly protected I dont envision any serious safety issues Best wishes n God Bless John T Too long retired EE |