Power wiring questions: grounding, circuit breakers

[K4RXR]

At the risk of opening the great power wiring debates again, I have some questions for the group:

1. When mounting radio equipment in a vehicle, is it better to do the grounding at the equipment or run the grounds back to the power source? Let's say you are tapping off the battery or other reliable power point underhood. Should I run a ground wire from the console back underhood or ground at the equipment? Is the body/frame of the vehicle a reliable enough ground?

2. Is there a downside, other than initial cost, to using appropriately-sized circuit breakers at the power source as opposed to fuses?

3. I going to have some equipment mounted in a console between the front seats plus a couple of Kenwood TK-x90 drawers remote mounted in the back of an SUV. It seems logical to run two separate power feeds from underhood to the two equipment locations. Should those two power feeds be protected with separate circuit breakers?

Thanks for your input!

Bob...

[tvsjr]

1. That depends. Here's the problem with going to the ground side of the battery. After a while, say the straps that bond the ground side of the battery to the body of the vehicle break down or come loose. When you go to crank, the starter flows the current to ground through whatever route it can... which may end up being body-->antenna mount-->radio-->battery. Obviously, Bad Things happen. If you're going to tap the ground side of the battery, you'll need to fuse the ground side of each radio appropriate.

2. I'm not a big fan of circuit breakers. Check this page:
http://www.bussauto.com/pdf/180.pdf
Note the Time vs. Rated Current graph. If I'm running a 150A breaker, the breaker will still allow 450A of current to flow for 10 seconds before tripping. I'd rather run a fuse that acts a tad bit faster. Personally, I use ANL wafer-type fuses commonly seen in car audio installations (I'm a dealer for Tsunami products, so I can get ahold of that stuff for reasonable money.)

3. Personally, I always run one big power feed (typically 1/0ga. in my POV) and distribute it at the radios. That gives you less wires to deal with and the expandability to add more things to the big power buss as you add equipment. I'd run a single 4ga. in your application, which would give you about 80A maximum capacity.

[kf4sqb]

I'll second tvsjr's opinion on this one. I will add that if you are worried about the integrity of the chassis ground, add a couple of extra ground straps from the battery's negative terminal to chassis, and from the chassis to the engine block. The current "main" ground connection should go from the battery to the engine block and then to the frame, although I think manufacturers are also adding a small-guage wire from the battery to the body these days.

[Jim202]

There are as many opinions about the ground side of a
power feed as there are so called experts giving their
opinion on here. There are several off shore radio companies
that just insist on adding a fuse to the ground side of the
radio feed wires.

Lets take a different look at this question. If the ground
between the battery is going bad, you will experience a
starter problem trying to crank the engine over long before
any damage is done to your radio equipment.

What do I base this on, about 38 years doing radio service
work. Let me go on to expand this statement. If this was
such a problem, don't you think that the major radio companies
like Motolrola, General Electric, RCA, MA-COM and a number
of others that supply radios to the public safety market would
have had problems along these lines.

There isn't a single commercial two way radio that has been
sold over the years with a fuse in the negative wire. The
only radios you see with a fuse in the negative side is the
"jap track" radios.

I have worked on fire trucks, dump trucks, tractor trailer
rigs, front end loaders, cement mixers, and all sorts of other
large engine vehicles. Don't you think that the two way
radio shops would have run into a problem along this line
already. It just doesn't happen.

About the only time I have seen a radio problem crop up
was when some dummy had a dead battery and tried to
jump start it. The radio problem shows up when the jumper
cables get connected up with the wrong polarity. Normally
the high current fuse blows due to the polarity protection
diode in the transmitter PA. Your not always that lucky with
the low current fuse for the control and receiver feed. Again
some dummy along the course of time would have a blown
fuse and replace it with the first thing they can find. This
ends up being a 20 amp fuse for a 3 or 6 amp circuit. The
result is burnt traces on the circuit board.

Bottom line is your waisting your time and the cost of a
fuse in the ground wire going to the radio. I have to put
this kind of talk from those on here as what you could call
old wifes tales. Ask one of them to provide a single
documented occurance of this happening to a commercial radio.

Most fleet service shops catch a problem with poor battery
connections and poor grounds long before and problems
develope in their rolling stock. If your having a problem
with your car or truck starting, you might start by checking
just how clean the battery terminals are. Have seen brand
new police cars have a problem with dirty battery connections.
This showed up with a high noise on the radio during
transmissions. It was solved by just cleaning the battery posts
and putting the connections back together. It also showed up
with problems starting the engine. It was cranking slow,
or wouldn't even crank once in a while. Slamming the hood
down was enough to jar the connection just enough to
allow the engine to start.

Jim

[kb0nly]

I always just put the ground to body near the radio, if you have a bolt that goes through body and frame use that if your worried about a solid body ground, but that can also be fixed with a ground from the negative battery terminal to the body which most newer vehicles have anyway. Nearly every vehicle i have worked on, late 80's and up, if they had fuel injection they usually had that added body ground due to the advent of control modules and computers.

Your just wasting your money running a ground from the battery back! In my current install i have a ground wire from the console up front to one of the seat bolts, on this van the seat bolts are welded to the floor with the nut up top and it provides a solid ground, and the radios are all grounded to a rear seat belt bolt that goes through the body and into the frame.

Another note, have your radios ignition sense connected so that it follows the practice of being off while the engine is cranking. I usually just tap the stereo circuit at the fuse panel, this way your radio is on in accessory, off with the key off, on with the key on, off while cranking, etc..

I have seen one case, in person, where the ground side fuse of a ham rig was blowing all the time because the body ground connection had failed underhood and most of the vehicles circuitry was using the radio as a return path. It didn't cause any damage to the radio, it just popped the fuse because the current being drawn was over the fuse rating. In this case the radio was grounded through it's mounting bracket so it became the return path without damage. However, it's very common for the radio to be mounted now days so that it isn't grounded directly due to all the plastic inside a newer vehicle and no metal dash to fasten to anymore! In that case the next available ground path is the coax and antenna, in theory this still should not cause damage to the radio since the coax connector, or if it has a pigtail off the back the shield of that coax, is grounded to the body of the radio and that is grounded to the ground lead, making the path from the ground wire out to the antenna. Sure, it could damage the coax by pulling a large amount of current through the shield, but it should not damage the radios internals because they are not inline if good engineering practices are followed.

Though there is an exception there as well, i saw one CB that was fried in this manner, the ground lead came in to the main circuit board and traveled a few traces before being connected to the radios chassis, so those traces burned off the board since they were inline with the radios chassis, but a wire jumper from the ground lead to chassis and it was running again without problems.

The best i can suggest is just body ground the negative lead on the radios, it's the method with less questions and possibilities for problems and is common practice. All the ham rigs out there still come with the fuse in the ground lead since most make the connection at the battery as the manual shows. I prefer to cut the ground and connect to the body anyway.

[firemedic2150]

Bottom line is your waisting your time and the cost of a
fuse in the ground wire going to the radio.

Bottom line is it is my radio, and my time, and I want a fuse on my main both ground and +ACC...and further more I fuse the ground and +ACC of each device.

My peice of mind is worth the couple of dollars to me.

Mark Mc.

[kb0nly]

Fusing the ground if not good practice though in my opinion, and i'm not the only one, all major aftermarket stereo systems and amp manufacturers, Motorola, GE, Kenwood, etc.. Funny that Yaesu puts the fuse in the ground lead on the ham rigs but not on the commercial Vertex rigs that i have had through here. If that fuse opens and the radio now runs by using the ground through the coax to the antenna mount you can cause damage as well as unreliable operation.

Fusing the ground is just stupid, and i am not calling you stupid for doing it, but this would be like putting a fuse in the ground of your home appliances. Yeah AC vs DC, but the fuse panel (breaker panel) is the common bonding point for the grounds of every device in the home, just like the vehicles body is the common bonding point for the ground on every device added.

If a fuse in the ground was a good idea the auto manufacturers would have put a fused link in the battery ground connection like they do with the positive feed. If the radios are grounded to the body/frame like all of the other vehicles electronics and the ground connection at the battery fails then nothing works, no potential for damage to the radios, if however you connect the ground of the radios to the battery then yes you should protect them with a fuse/breaker, but as i mentioned it's really not that good of a practice to ground directly to the battery. A lot of times that i had to deal with noise and voltage drops it was due to a battery rather than body/frame ground.

But i guess we have beat this horse enough, and this is not the first time on here either! In a post on one of the Motorola email reflectors a few months back an electrical engineer got in on the conversation as well, i would take his word, along with my personal experience, over anyone else's opinion.

[K4RXR]

Thanks for all of the tips and advice.

Note that I said nothing in my original post about fusing the ground lead. My question was whether or not to ground to the body/chassis of the vehicle at the equipment or run the grounds back to the underhood electrical distribution point. Based on what I read here, I am going to head down the path of grounding at the equipment. I'll also make sure that the ground straps between the battery and the body (I'm dealing with a separate body on frame vehicle) are in good shape.

Also note that I will have equipment in two separate locations in the vehicle. My current thinking is to run separate B+ feeds with separate fuses from the power distribution point underhood to those locations.

As always, the posts here give a guy lots to think about.

Bob...

[kb0nly]

Note that I said nothing in my original post about fusing the ground lead.

Nope, but that always comes up when grounding at the battery versus grounding at the equipment location is mentioned.

It sounds like your well on your way. With more than one equipment location i would suggest running a good heavy gauge power supply protected by fuse or breaker at the battery to the console, then branch out from there. What i did was put an underhood breaker feeding a 4awg B+ feed to the console which contains a eight position fuse panel for all the items powered at the console, then the radios B+ leads are brought from the back to the console where they are connected to breakers which are fed by the B+ connection at the fuse panel. This keeps the wiring simple and eliminates having to run more than one smaller feed from the battery.

Here are the pictures of my install.

http://frontiernet.net/~kb0nly/mobile.htm

[Birken Vogt]

A little late but:

If it is low power such as most two-way radios I will cut the ground wire as short as possible and screw it into the nearest substantial metal that is grounded to the chassis. The current requirement for any mobile radio, even "high power" ones are not all that great. If you are really worried about it then check available voltage at the radio power plug during transmit and see what the drop is like. When you run a commercial shop there is no way it would be worthwhile to run a long ground wire to somewhere to prevent maybe one voltage drop problem in a couple hundred installations. Just deal with it if it comes up. Make sure it works right before letting it out the door/leaving though!

If it is high power such as a light bar, etc. then I will make certain to ground all radios, lights, etc. to the same point, usually a threaded stud sticking up from the floor pan or something capable of high current. Then I will also make certain that the ground path from that stud or whatever back to the battery is quite sufficient and upgrade it if necessary. The last one I did I think I used a seat belt stud for grounding which goes to the floor pan, then there was a heavy ground strap from the firewall to engine block, good enough. Also it helps to have a clamp on DC ammeter so you can verify that the ground current is flowing through the path that you think it should.

Birken