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ContinuousWave: Small Boat Electrical
Wiring Practices: Terminal Posts: Stacking Ring Terminals
|Author||Topic: Wiring Practices: Terminal Posts: Stacking Ring Terminals|
posted 09-18-2014 11:49 PM ET (US)
Terminal posts or terminal studs are often provided as connection points, typically on older-style marine batteries and on bus bars. Connection to terminal posts should always be made with RING terminals. The best practice is to limit the number of ring terminals on a terminal post to one, but if that is not possible the terminals can be stacked. Opinions vary on the maximum number of stacked ring terminals on a terminal post. Some publications proscribe not more two terminals while others suggest as many as four can be allowed.
There does not seem to be any applicable federal regulations about stacking ring terminal connectors on a terminal post on a boat. There are federal regulations about electrical wiring, but they seem to be silent on the question of the maximum number of ring terminals allowed on a terminal post. The regulations also do not apply to boats with outboard engines, so even if there were some advice in them, it would not be binding on outboard engine boats. I browsed through several sections of federal regulations related to boat electrical wiring, but did not find anything on the topic. Perhaps someone can find something, if I overlooked it. See:
Another source of advice, although not legally binding unless specified in some state regulations, is the American Boat and Yacht Council. They suggest a limit of four ring terminals. See E-188.8.131.52.11 in
An aircraft related website has quite good information on using ring terminals. Aircraft are much more closely regulated than recreational boats, and work practices are typically much stricter. However it seems that even on aircraft one can have four ring terminals on a terminal post, although there is a very specific method of assembly that is prescribed. See the section on terminals in this publication, split into two parts:
There are some excellent illustrations in that reference that show the best method of assembling ring terminals for stacking, including details about proper orientation of the ring terminals and use of flat washers and lock washers to make a secure electrical and mechanical connection.
I believe that the national electrical code requires that only one conductor should be attached to an electrical terminal. I think this is meant more for bare wires being placed under a compression terminal, not exactly for ring terminals on a terminal post, but the concept is similar. (If anyone is really expert on the national electrical code, you might comment on this.)
posted 09-19-2014 12:02 AM ET (US)
Regarding making connection to a terminal post on a battery, it is here that the rule of only one ring terminal seems to be most appropriate. I base this on the practices seen in automobiles. The connection to a battery in an automobile often involves more than one conductor, but the conductors are assembled into one connector. This is very common on the old style auto battery with the tapered lead posts. Only one connector can fit on those posts. On the GM-style side terminal batteries, I have seen a stacking of connectors, but never more than two. It seems that only on the marine-style batteries with threaded terminal posts does one find it fairly common to have more than one ring terminal on the terminal post, but that is often in owner-added installation.
I note that Evinrude has revised their outboard engine battery cables so they pre-assemble two conductors onto one ring terminal for connection to the battery. They took this approach because there were many problems in the field caused by boat owners or installers stacking up ring terminals on the battery posts.
The purpose in avoiding more than one ring terminal on the battery post is to get a more secure mechanical and electrical connection. Connections using many stacked terminals are generally more prone to becoming loose, and a loose connection at the battery can cause damage to the boat electrical system.
posted 09-19-2014 12:40 AM ET (US)
On those threaded posts, maybe you should add that the wing-nuts that came with the batteries must be thrown out and replaced with ny-lock type hex nuts, thus eliminating a lot of loose connection problems.
posted 09-19-2014 09:10 AM ET (US)
Wing nuts should not be used. Nylok or nylon elastic stop nuts are controversial. The plastic material in the nylok nut insulates the electrical connection between the terminal post and the metal part of the nut. Also, if the terminal becomes hot, as sometimes happens, the plastic could soften or even melt. And the locking property of the plastic occurs only on its first use; if reused there is less locking.
I think one could have a long discussion on the just the fastener to be used on a terminal post [in a separate thread, please].
posted 09-19-2014 09:12 AM ET (US)
A recent Sail magazine paragraph and photograph warns that more than four conductors attached to a battery terminal is ill advised. Saw this yesterday in the [physician's] office awaiting a flu shot. It was painless by the way,
posted 09-20-2014 02:33 AM ET (US)
[Changed topic to a new topic. Please stay on this topic. We are discussing the maximum number of ring terminal connectors to be used on a single terminal post. Thank you for staying on this topic.--jimh]
posted 09-20-2014 09:08 AM ET (US)
My cottage in the north woods is off the power grid, so I make my own electricity by both solar and a propane generator that charge a bank of 20 6-Volt deep-cycle batteries. My battery guy says that all of them should have SS lock nuts on them because the normal cycling of the batteries will loosen the terminals. I had one fail, the terminal stud actually melted and the post slid out of its molded lead base. The situation is worse in boat with all of the normal vibration from the engine and operation afloat.
posted 09-20-2014 10:35 PM ET (US)
What is the mechanism that loosens the fasteners on the battery terminal posts? Is it from heating and expansion, then cooling and contraction? The fasteners on an engine are subject to much wider heat ranges and they are not all stainless steel. What properly of the stainless steel is the antidote to the battery's action in loosening. I don't quite see the connections, to make a little pun.
There is an interesting video that shows the effect of torsional forces on fasteners and loosening them, with two different kinds of lock nuts. A special machine, a Junkers Machine, is used to create repeated torsion forces. Watch the results here:
Note that with the torsional movement test, the use of the very common helical split washer (lock washer) actaully caused the fastener to loosen sooner than without the washer.
The same firm, Bolt Science, has also produced this poster to show more about the self-loosening of fasteners:
Note that stacking of ring terminals would seems to be an excellent way to introduce more torsional movement on the fastener. Vibration transmitted through several wires connected to the battery terminal could contribute to self-loosening.
posted 09-22-2014 11:53 AM ET (US)
[Sidebar on unusual fasteners for electrical terminal posts which are not recommend and unusual ways to tighten the unusual fasteners has been deleted.--jimh]
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