NAC3 cables

[lustyd]

I’m planning the install of my new NAC3 autopilot and looking at cables which seem to need to be round to seal in the rubber grommets on the unit. It’ll drive a Raymarine Type 1 linear unit which seems to top out at 3A but I’ve found some Oceanflex 2x2.5mm and 3x2.5mm 29A cable which looks a reasonable fit. The NAC is rated higher than this at 30-50A. I’m thinking to put a fuse on rated to the cable and assume the load will never go higher with this drive unit. Steering is very light anyway so doubt I’ll approach the max amps of the drive unit.
alternative is larger cable but individual cores which feels like a faff to install and will create unnecessary wiring mess.
anyone fitted similar or have thoughts on the plan? Termination is in some nice screw terminal plugs so it’s all bare wire including the NMEA.

 

[PaulRainbow]

Cable size will depend on the length of the cable, it'd need to be very short for 2.5mm. How far between the drive and the computer ?

For fusing, you should fuse for the drive, not the cable. If anything were to jam, or the motor was overloaded for any reason, you want a fuse to blow or a breaker to trip, rather than damage the drive or burn the motor out.

 

[mrangry]

I’m planning the install of my new NAC3 autopilot and looking at cables which seem to need to be round to seal in the rubber grommets on the unit. It’ll drive a Raymarine Type 1 linear unit which seems to top out at 3A but I’ve found some Oceanflex 2x2.5mm and 3x2.5mm 29A cable which looks a reasonable fit. The NAC is rated higher than this at 30-50A. I’m thinking to put a fuse on rated to the cable and assume the load will never go higher with this drive unit. Steering is very light anyway so doubt I’ll approach the max amps of the drive unit.
alternative is larger cable but individual cores which feels like a faff to install and will create unnecessary wiring mess.
anyone fitted similar or have thoughts on the plan? Termination is in some nice screw terminal plugs so it’s all bare wire including the NMEA.

I am looking at the NAC3 can I ask where you bought it from

 

[lustyd]

Thanks Paul, the run between the computer and the drive will be a metre or so and not an issue at all. The run with the power cable from the switch panel is around 6m so in theory also not an issue given the very low current required. It's shared with the helm though so I may uprate the run to the stern and then split off into two smaller guage runs to the AP and to the helm instruments. Alternatively I could run from the main switch at the steps directly to the stern and bypass the switch panel for the AP only.
I had considered that for the fuse but unsure what extra load the AP computer places on the circuit so perhaps better to add a second, smaller fuse between the AP and drive? The AP computer can handle more than the cable so the AP itself seems safe. The manual has no info on any of this. Obviously I'd then be making troubleshooting much harder, especially since it's all in the stern behind some panels.

 

[lustyd]

I am looking at the NAC3 can I ask where you bought it from

I bought the core pack from Force4. I had to order it in but I think they now have some stock - it came in 2 weeks ahead of schedule. They seem to be cheapest retail price about, and also I've bought most of the system from there so simpler for warranty issues with one throat to choke so to speak.

 

[PaulRainbow]

Thanks Paul, the run between the computer and the drive will be a metre or so and not an issue at all. The run with the power cable from the switch panel is around 6m so in theory also not an issue given the very low current required. It's shared with the helm though so I may uprate the run to the stern and then split off into two smaller guage runs to the AP and to the helm instruments. Alternatively I could run from the main switch at the steps directly to the stern and bypass the switch panel for the AP only.

2.5mm from the computer to the drive will be OK, but it's too small for the 6m run to the computer, for a 6m run i'd use 4mm. As suggested, you could run bigger cable aft, then split close to the computer. But if you did, use 6mm. Fuse the two supplies where they split. The NAC2 has a 30a internal fuse, so i'd fuse the 6mm cable at source, then, where it splits, fit a 30a fuse for the NAC3 and whatever is appropriate for the instruments.

I had considered that for the fuse but unsure what extra load the AP computer places on the circuit so perhaps better to add a second, smaller fuse between the AP and drive? The AP computer can handle more than the cable so the AP itself seems safe. The manual has no info on any of this. Obviously I'd then be making troubleshooting much harder, especially since it's all in the stern behind some panels.

I'd expect the 30a internal fuse to blow if the drive tries to overload the computer, but it wouldn't hurt to fit a lower rated fuse between the computer and the drive.

 

[lustyd]

For some reason I was thinking it would protect the drive, but I see your point and the realistic scenario is that the drive would already be fried so I'll probably keep it simple there and leave out the extra fuse.

Given the short run I'll probably bin the multicore as that won't drastically simplify anything that a bit of split conduit can't fix. The only reason for that was to have a larger round cable to go through the rubber grommet and keep the IP rating (it's going in a stern locker). I think 6mm might be too thin to make a good seal there but I'll check when I get to the boat. Now I'm thinking about the 6mm I don't think it will be too cumbersome to do the split in the switch cupboard, it's pretty thin cable so hopefully the conduit has room. I'll be removing some old cables for the remote mic and ST1 but replacing with Ethernet and NMEA so fingers crossed!

Thanks for the discussion, sometimes it's hard to see the obvious stuff!

 

[PaulRainbow]

For some reason I was thinking it would protect the drive, but I see your point and the realistic scenario is that the drive would already be fried so I'll probably keep it simple there and leave out the extra fuse.

Given the short run I'll probably bin the multicore as that won't drastically simplify anything that a bit of split conduit can't fix. The only reason for that was to have a larger round cable to go through the rubber grommet and keep the IP rating (it's going in a stern locker). I think 6mm might be too thin to make a good seal there but I'll check when I get to the boat. Now I'm thinking about the 6mm I don't think it will be too cumbersome to do the split in the switch cupboard, it's pretty thin cable so hopefully the conduit has room. I'll be removing some old cables for the remote mic and ST1 but replacing with Ethernet and NMEA so fingers crossed!

Thanks for the discussion, sometimes it's hard to see the obvious stuff!

The internal fuse should blow if the drive is overloaded, but it's a 30a fuse, a lower rated one would blow faster. But, there's probably not much difference.

If you want to run a pair of cables through a bulkhead using a gland, the Scanstrut ones come with a blank that you drill yourself, for example: Scanstrut Cable Gland Deck Seals | ASAP Supplies

 

[lustyd]

The gland is built in to the NAC 3 as you can see in this image. It's a sheet of "rubber" with gaps for wires. Each hole is actually still sealed and you have to break the seal to push a cable through, ideally a close fitting cable to keep it sealed. The unit is IPx5 rated but obviously that requires this seal to be intact. In the image it looks plastic, but it's a relatively soft and stretchy rubber.