Extending a cable

I’m installing an AC subpanel to create two separate feeds—one (15 amps) for a cooktop and the other (20 amps) for a convection/microwave oven. The cable that feeds the subpanel from the main panel is 8 mm three-wire. It’s in excellent condition, but very stiff, which makes it difficult to wire the panel inside the polycarbonate box I’m using to house the subpanel. I’d like to extend it a couple of feet with more flexible number 8 boat cable—which will be much easier to make connections inside the box.

What’s the preferred way of doing this: install a terminal block to make the transition or use heat-shrink butt connectors? (I don’t want to replace the 8 mm cable unless both of the above are patently unsafe.)

All AC splices or terminal blocks need to be inside NEMA enclosures. Plus it is generally bad practice but within code to make such extensions.

I would replace that cable sized consistent with whatever breaker is protecting the wire or bigger and at least 8 gauge.

David

I think you may run afoul of the ABYC wiring standards. For instance, if you extended it in your home you could run the ends into a 2x4” electrical box and use wire nuts to connect the wires. However, all boat connections must be mechanical and sealed, so that seems to say you could use a marine butt connection with a shrink plastic cover then the connector and an inch or so of wire covered with marine shrink tube. Here’s where I have a problem with that, even if it meets the standard. You note that the existing cable is stiff which to me suggests some hardening of the insulation caused by heat generated by resistance in the wires. Then there’s the state of the art of the wire. I’m betting that it’s stranded plain copper which we all know tends to corrode. I know it’s a PITA, but if it were me, I’d replace the cables with new marine tinned cable.
That’s a great looking boat by the way. Btw, those amperages seem backwards. Are you sure the cooktop is only 15 amp?

I would just replace the entire cable if the one there is accessible Pcpete suggested above.

Thanks, all. The cable is stiff because the individual wire strands are thicker than the strands used in the finer flexible marine cable you find today. It’s very bright copper and there’s no evidence of corrosion or of it ever overheating.

The cooktop is a two-burner induction unit and indeed only requires a 15-amp breaker.

Not sure why ABYC would prohibit the use of a properly rated terminal block with cover. Every AC circuit on the boat—positive, neutral and safety ground—currently goes through terminal blocks before being routed to various loads.

You could do either a butt connector or a junction strip. I would probably go with the junction.

I would split this into two circuits of 20a each with 12/3 boat wire. The original wire is not boat wire. Not illegal but hard to work with.

Like Comodave said, a marine approved junction box is an acceptable practice. None of us know if the existing wire is to current standards. If it was installed by the builder then it is to the standard your insurance company has accepted.

I was able to reach an ABYC electrician I know and he explained the standards; so I will be using a terminal strip inside a covered junction box to extend the existing cable. That wire is definitely boat cable that was commonly used in late 80s Defevers and many other trawler-types. The entire boat is wired with it. I always replace any of it that looks corroded, but this one is bright and shiny.

Thanks again for the advice.
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tiltrider1 said:

Like Comodave said, a marine approved junction box is an acceptable practice. None of us know if the existing wire is to current standards. If it was installed by the builder then it is to the standard your insurance company has accepted.

Click to expand...

While that might be good practice, ABYC recommends using insulated butt crimp connectors for splicing. Insulated crimp connectors are common for #8 wire and readily available for splicing. Personally I would not hesitate using a wire size rated insulated splice terminal block inside a panelboard. And remember, ABYC suggestions are not LAW!

I vote the terminal strip in a box too...I bet it is acceptable under ABYC tandards if the connectors, etc inside the box meet the applicable ABYC standard.


Here's but a few AC system snipits from ABYC....there may be additional pertinent items...did"t see any but I scanned quick.



11.14.5.3 Each splice joining conductor to conductor, conductor to connectors, and conductor to
terminals must be able to withstand a tensile force equal to at least the value shown in Table XV for the
smallest conductor size used in the splice for a one minute duration, and not break.



11.14.6 INSTALLATION - GENERAL
11.14.6.1 Junction boxes, cabinets, and other enclosures in which electrical connections are made shall
be weatherproof, or installed in a protected location, to minimize the entrance or accumulation of moisture or
water within the boxes, cabinets, or enclosures.
11.14.6.1.1 In wet locations, metallic boxes, cabinets, or enclosures shall be mounted to minimize the
entrapment of moisture between the box, cabinet, or enclosure, and the adjacent structure. If air spacing is
used to accomplish this, the minimum shall be 1/4 inch (7.0 mm).
11.14.6.1.2 Unused openings in boxes, cabinets, and weatherproof enclosures shall be closed.
11.14.6.2 All conductors shall be supported and/or clamped to relieve strain on connections.