Electrical Materials & Connections

[CapetaniosG]

The information I'll outline below is intented to raised awarness and educate.
Take it for what it is worth.

The most common materials used for electrical connections in marine electrical systems, are copper, brass, bronze and stainless steel (SS). That is widely known to most of us in boating.

What is not widely known, is how these materials behave when they become part of a boat's electrical system and how they may affect the safety of your boat.

Copper is the standard material for electrical systems such as electrical wire, bus bars and terminals found in a boat's electrical system. But many of us have seen and used, other materials such as bronze, brass and SS in making electrical connections aboard our boats. I bet if we were to examine our boat's electrical connections we'll find a good number of them containing either bronze of brass (bus bars) or SS (SS bolts and washers) or all three.

It is not widely known that SS has 3 to 5 percent the conductivity of copper and bronze as low as 7 to 10 percent. Brass has a conductivity of less than 30% compared to copper. In other words, these materials are poor electrical conductors.

In practice what this means, is that a SS bus bar has to be over 3000 times the size of a copper bus bar to carry, safely,the same electrical load and a brass bus bar has to be 3 to 4 times the size of a copper bus bar to cary the same electrical load. The result is that if an undersized bus bar, made of one of these materials, is used it can become very hot and cause a fire. The reason is that we introduce a high resistor into the electrical system which can affect the operation of equipment or cause a fire. The same logic holds true, not only for bus bars, but for every type of electrical connections we use these materials to make.

For example, if we use a SS washer between an electrical terminal and a copper bus bar, what we have done in effect, is to introduce a high resistor
in the circuit which, under certain conditions, can get very hot and cause a fire or adversely affect equipment operation.

It should be noted here, that due to the fact that there is no short circuit in such a connection, a fuse or a circuit breaker will NOT protect against this kind of fire, if there was to be one.

Electrical connections must be clean and tight. If they are not clean, they can NOT conduct readely and safely the electrical load. If they are loose, they will create arcing, when current flows thru them. The more the current flow the greater the arcing and the greater the risk of fire. Here again, a fuse or a circuit breaker will NOT protect the circuit or your boat.

So, be careful when choosing and using materials to be used in electrical circuits. Your life or the safety of your boat may be at stake.

CapetaniosG
Hatteras 53MY

[Walter P]

Thank you so much for your explaination regarding resistance. I frankly admit to a very limited knowledge base for things electrical and as a result I have a deep respect bordering on fear about it. On my 3 page llist of things for Tom Slane's shop to do for me is a thorough going over of my entire electrical systems and make repairs and improvements as needed.

Walt P.

[Nonchalant1]

Just 2 questions:

1. Did not Hatteras use a lot of brass terminals connecting copper wires to copper busses?

2. Is there a conductivity issue with aluminum? Particularly the aluminum commonly used for crimp type butt connectors?

Thanks,

Doug

[Traveler 45C]

All good points and thanks for bringing up this food for thought. I can't wait to see how this one turns out.

So the "bad" metals don't conduct as well as copper, thats ok. If you add them all up I don't think that a washer here and an Alum crimp there is going to add significant resistance to the house loads.

Dirty connections or using the wrong guage wire would be far more harmful.

[harnett]

Couple of points to add

1) all the decent quality crimp terminals are tin plated copper not aluminum

2) Hatteras did use unplated brass bus bars and connections. Had problems with them and learned better. Now they don't use it. These have caused documented fires.

3) I agree dirty connections and unsuffienctly size wire are bad but if the current passes through a high resistance connection of brass or stainless it will cause the same problem as the other two issues.

4) The original point of brass and stainless being poor conductors is very valid and that is why Hatteras no long uses it for electrical connections. I believe they are still boasting that fact in their sales information.

If given the choice or doing repairs, go with tin plated copper if you can, tin plated brass is ok just size accordingly.

[Boss Lady]

the real technical issue is to ask what is carrying the current load? If you have good conductor to conductor contact then it is less important what you are mechanically joining them with, but if it is a buss bar, or crimp connector and is actually part of the circuit then it is important what metal it is. The same rule applies to grounding and bonding contections. Use the wrong metal type or size and you have an instant resistance heater element instead of the good conductor you thought you had installed. It may carry the load, but it can become red hot and start a fire. There are plenty of sources to find what size wire gauge you need for a given circuit, you need to know what the load in amps is and the voltage, plus the length of the wire run. You must select a wire gauge that will not allow more than a 2% voltage drop, this applies to DC and AC circuits. Bigger is better. Don't assume that an electrical component is ok to use just because it is for sale at the local supply house or is original to the boat. Remember aluminum house wire? That stuff burned down quite a few buildings before they figured out that aluminum turns into aluminum oxide (an insulator) creating a huge resistance at connection points. I clean any new connection and coat it with NO-OX to protect it from the elements and maintain a good electrical connection. Which is something the manufacturers don't do but should.

thanks for the safety message!

[Nonchalant1]

Thanks - Now can I ask a dumb question?.............How come it's OK to have those huge shotgun shell fuses carrying 50 amps at 32 volts, and they're just connected to the equally huge cables by thin copper leaf spring holders? The surface area touching the brass or brass plated fuse ends must be very small, but they don't get hot.

Doug

[doc g]

I've got a question. I have a bank of 2 trace inverters. Last weekend I woke up to the dreaded smell of something electrical burning. The ac input to one of the inverters had melted and burned off. It is a big copper wire and goes into a buss bar on the inverter. The wire is nearly as big as the hole in the junction block. The J block appears to be steel which has a big screw in it that bites the wire. I was thinking of tinning the wire(s) with solder and then putting them back in the J block. Also thought of using a crimp connector to clamp the end of the wire down so I know that it is all the way into the j block clamp and that I've got all the wire securely in the screw clamp. What will the solder do vs. using a crimp on the end of the wire vs. bare wire. I obviously do not want this to happen again. Any help from the electrical experts wuold be greatly appreciated!!!!...................Pat

[harnett]

If your connector is what I think it is from the description, ie a hole in a piece of metal into which a large set screw acting screw applies pressure to the wire you are better off with the straight stranded wire. No crimp, No solder. This is a common connection on electrical panels. The design is to actual spread out the wire to force a greater contact area with the block. The likely problem with this is as follows. The metal block with the hole in it is probably aluminum. When current is flowing it warms up. Then cools down when no current is flowing. Repeated cycling causes the screw to loosen. Less contact between the wire and block. More heat, eventual melt down. The solution, check the tightness of the screw on a periodic basis. By the way, this should also be done in home electrical panels every few years. With no power on of course. Same type of connection.

[harnett]

I forgot to reply to the "shotgun shell fuse question". I'm generalizing since I can't see you exact installation but here goes. The blades on most of these fuse holders are curved to conform to the shape of the fuse. ie large contact area between the fuse and holder. The fuse holder has a ampacity rating. Let's assume it is good for the 50 amps mention. If so then the cross sectional area of two blades combined will be good for 50 amps. Assuming a properly selected componant, I'll bet if you mic the thichness of a blade times the length, then times 2 each side), then times the contact area it will be as much or more than a equal capacity wire. By the way even a holder rated at 50 amps may not be 50 amps continuous and you would seldom see that on your boat any way. Sorry to bore everyone with electrical stuff that you probably really didn't want to know anyway.