reb78 Posted July 9, 2015 Share Posted July 9, 2015 Quick question about adding electrical accessories and the earth requirements. The example in mind is my amp. It is in the battery box and so i have taken the positive from the battery via a fused link and then earthed it directly back to the battery terminal. Is this ok or is there any reason the earth should not go to the terminal but the body (say a bare metal bit on battery box) instead? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 9, 2015 Share Posted July 9, 2015 Nope, that's fine, in fact better Quote Link to comment Share on other sites More sharing options...
ejparrott Posted July 9, 2015 Share Posted July 9, 2015 Best way. My raptor dash has a couple or earth wires in the loom, all going back to the battery or a terminal rail in the battery box that is connected direct to the battery Quote Link to comment Share on other sites More sharing options...
HoSS Posted July 9, 2015 Share Posted July 9, 2015 Taking 'parallel' earth cables back to the battery has one flaw. Obviously a major principle of any wiring system is that cables in a particular circuit must be able to carry the currents of that circuit, or be protected by a fuse device. In the case of extra positive feeds taken from a battery these would be fused and the upstream cable well protected (or more correctly using high temperature fire resistant cable). All ok. In the case of a conventional vehicle (or house) wiring system there is a common ground (neutral) where load circuits 'star' out from. If one of the load grounds has a fault you lose that circuit. If the incoming battery cable becomes loose/broken you lose all circuits. All good. Now, if you take extra grounds directly to the battery (in parallel with the high current battery lead going to the star point) and then subsequently the battery ground cable becomes loose, all of the vehicle current may try to flow through your parallel grounds, thus resulting in them burning. Yes its uncommon that a battery cable fails, and a lot of people do it. But its a flawed design to bypass the 'star' point. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted July 9, 2015 Share Posted July 9, 2015 I connect mine to the vehicle locally as well as running them back to battery. See what you're saying though. Quote Link to comment Share on other sites More sharing options...
Dads Toy Posted July 11, 2015 Share Posted July 11, 2015 So each item should only be earthed via the "star" (header) or direct to battery, not both. Is that correct? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 11, 2015 Share Posted July 11, 2015 I understand what HoSS is saying, but in this instance, given the cable is already right by the battery, you go straight to the battery, otherwise you are just making another connection point to fail. Quote Link to comment Share on other sites More sharing options...
HoSS Posted July 12, 2015 Share Posted July 12, 2015 So each item should only be earthed via the "star" (header) or direct to battery, not both. Is that correct? No, it should really only be done to the star point or chassis. If you do it directly you are creating a parallel path. I understand what HoSS is saying, but in this instance, given the cable is already right by the battery, you go straight to the battery, otherwise you are just making another connection point to fail. It doesnt matter where it physically is ( I presume you mean the load ground) If you terminate directly to the battery you risk a parallel ground path. Take the example of ejparrot above. The raptor dash ground comes from the battery, to the dash, and probably regrounded to a sensor or two around the vehicle. If the main battery ground breaks, the this will burn those grounds, possibly the dash internals. There is a reason why all cars come from the factory with this design, if you bypass it you take a risk. p.s. Theres another reason not to do it in the case of instrumentation too. The main battery ground will have current flowing along it, which means there will be voltage drop. You will add inaccuracies or noise to your instruments. Its the reason a common (chassis) ground is used. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 12, 2015 Share Posted July 12, 2015 The amp is in the battery box with the battery, if you read the original post. Quote Link to comment Share on other sites More sharing options...
HoSS Posted July 12, 2015 Share Posted July 12, 2015 The amp is in the battery box with the battery, if you read the original post. I did read it. You don't seem to understand. The amp is grounded to the battery, and probably by its case fixed to the chasiss/body. If the battery cable to the chassis fails, vehicle/engine current will pass through the amp = not good. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 12, 2015 Author Share Posted July 12, 2015 Sorry. I didn't think I would create such a discussion. My amp is in the battery box as Bowie points out. It takes a fused live from the battery and it made sense at the time to earth it directly to the battery. Recently, it has been working slightly intermittently sometimes will be fine for a week and other times might work for ten mins and turn off. I think there is a fault with the amp but, whilst reading around, I came across an argument on an ICE site that they should be earthed to the chassis/vehicle, not directly to the battery. It didn't make sense why and no one explained why in that thread, or if it would really be a problem with my current setup, hence my question. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 12, 2015 Author Share Posted July 12, 2015 I did read it. You don't seem to understand. The amp is grounded to the battery, and probably by its case fixed to the chasiss/body. If the battery cable to the chassis fails, vehicle/engine current will pass through the amp = not good. It's actually mounted on a piece of wood in this instance so probably no problem with parallel earths in this case I guess. Perhaps the wood is what is causing the fault as I guess it could be getting hotter than if it were mounted to metal? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 12, 2015 Share Posted July 12, 2015 I understand perfectly well. It is evidenced very well, for example, in an earth strap failing and a melted handbrake/throttle cable. Seems to me you're describing a problem that is extremely unlikely to exist, and given that a massive amount of electrical accessories, even in just this forum, are wired straight to the battery, including pre-wired accessories (e.g ARB compressor wiring diagram does exactly this), and the fact we don't have electrical fires reported every week on here leads me to a conclusion it's extremely unlikely to be an issue. As for the amp problems, be good to trace each of the audio and power wires, and switched live/radio amp remote to look for damage, check/clean connectors for loose wires/corrosion, otherwise swap out another amp, could well be an internal issue. I'd be surprised if the amp was designed only to be clamped to metal, most of them get screwed down to a boot floor with carpet underneath, with no issues at all! Quote Link to comment Share on other sites More sharing options...
need4speed Posted July 12, 2015 Share Posted July 12, 2015 Sorry for the hijack Richard but I'm in a similar situation. I have a 50mm Earth from starter bolt, 35mm Earth from bolt in chassis outrigger, and a 16mm Earth from a stud in the bulkhead all running back to a stud on my main negative busbar (which is connected to negative terminal on my main battery). Given the current discussion regarding earths all going to battery negative, is my setup alright or am I in for future problems? Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted July 12, 2015 Share Posted July 12, 2015 Having become an expert in birds nests and dodgy multiple joints, I now just give each accessory it's own fused supply and earth on the battery with twin core of the appropriate size. Mo Quote Link to comment Share on other sites More sharing options...
HoSS Posted July 12, 2015 Share Posted July 12, 2015 In my first reply i agreed that its unlikely to have a battery cable fail. But it can happen. Why do it the wrong way way when you can do it correctly. This is apart from the fact that it may cause problems with instruments due to ground voltage drops. Anyway, i have given my input as a qualified professional electrical engineer, you are of course free do do it any way you wish. Need4speed - yours sounds ok, as you have a common ground with large cable. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 13, 2015 Author Share Posted July 13, 2015 Sorry for the hijack Richard but I'm in a similar situation. I have a 50mm Earth from starter bolt, 35mm Earth from bolt in chassis outrigger, and a 16mm Earth from a stud in the bulkhead all running back to a stud on my main negative busbar (which is connected to negative terminal on my main battery). Given the current discussion regarding earths all going to battery negative, is my setup alright or am I in for future problems? No worries Phil. I think I need a new amp, so if this thread is useful to others then feel free to expand it. Quote Link to comment Share on other sites More sharing options...
Anderzander Posted July 13, 2015 Share Posted July 13, 2015 How does this play into dual battery set ups ? As I presume they put in parallel path by default ? Quote Link to comment Share on other sites More sharing options...
landroversforever Posted July 13, 2015 Share Posted July 13, 2015 Both earths on a twin battery system will be joined anyway Quote Link to comment Share on other sites More sharing options...
AMB Posted July 13, 2015 Share Posted July 13, 2015 In my first reply i agreed that its unlikely to have a battery cable fail. But it can happen. Why do it the wrong way way when you can do it correctly. This is apart from the fact that it may cause problems with instruments due to ground voltage drops. Anyway, i have given my input as a qualified professional electrical engineer, you are of course free do do it any way you wish. Need4speed - yours sounds ok, as you have a common ground with large cable. As another professional engineer, I agree entirely. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 13, 2015 Share Posted July 13, 2015 ...and as another 'professional engineer' I'm not disagreeing with you, only pointing out the likelihood is remote, and if accessory manufacturers don't do it why should joe public be that bothered? Anyways.... enough willy-wanging Quote Link to comment Share on other sites More sharing options...
AMB Posted July 13, 2015 Share Posted July 13, 2015 ...and as another 'professional engineer' I'm not disagreeing with you, only pointing out the likelihood is remote, and if accessory manufacturers don't do it why should joe public be that bothered? Anyways.... enough willy-wanging Possibly because a lot of automotive and accessory manufacturers are either not particularly good at electrics, design down to a price or write manuals for joe public - witness LR design! or Lucas in general. My point was more to do with earth loops/offsets causing issues with lower power electronics and instrumentation than with battery cable failure. Quote Link to comment Share on other sites More sharing options...
need4speed Posted July 13, 2015 Share Posted July 13, 2015 Willy-wanging... Lol Quote Link to comment Share on other sites More sharing options...
jumping jack Posted August 11, 2015 Share Posted August 11, 2015 Back to the point, amps do need to be isolated from the chassis / common earth. by which I mean the amp body, not the earth terminal. I know you said it's mounted on a wood sheet (which won't be causing problems with overheating), but are the mounting screw touching the body work? That can and does cause problems with the amp cutting out randomly amount other problems. Quote Link to comment Share on other sites More sharing options...
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