Small Busbar connections.

[mitiempo]

Originally Posted by coopec43

Thanks Jammer! Your points are a whole lot clearer now.

Now, is there a disadvantage (apart from cost) in using very much oversize cables?

Oversizing a wire always makes sense, within reason. One size up from the Blue Seas (or similar) chart costs little. Wires should never get warm much less hot. If the wire gets warm in normal use it is too small for the load. One size up is not a problem as far as flexibility of wire is concerned.

Ampacity and practical use are very different. 10 awg 105 degree stranded copper has an ampacity of 60 amps according to Blue Seas. I would never use it for more than 30 amps intermittently and 20 amps continuous.

Note: Blue Seas busbars are 10/24, not 10/32.

ABYC allows up to 4 lugs on a post. I like to keep to 2 maximum.

[coopec43]

Originally Posted by mitiempo

Oversizing a wire always makes sense, within reason. One size up from the Blue Seas (or similar) chart costs little. Wires should never get warm much less hot. If the wire gets warm in normal use it is too small for the load. One size up is not a problem as far as flexibility of wire is concerned.

Ampacity and practical use are very different. 10 awg 105 degree stranded copper has an ampacity of 60 amps according to Blue Seas. I would never use it for more than 30 amps intermittently and 20 amps continuous.

Note: Blue Seas busbars are 10/24, not 10/32.

ABYC allows up to 4 lugs on a post. I like to keep to 2 maximum.

Thanks for that advice.

"ABYC allows up to 4 lugs on a post". I wasn't aware of that. If I have exceeded 4 it would be very low amperage.

[Boatwright]

Never fail conservative rules of thumb:

No matter what the load use a minimum of #14 wire for lighting, small pumps, etc.. This is for mechanical strength and security of terminals.

Busbars and terminal strips should be #8 or larger. #6 screws are too small, mechanically weak, and too easy to twist off with a screwdriver.

#14 wire - Use #8 terminals. Maximum 15 A fuse or breaker. Circuit load should be 12 A max.

#12 wire - Use #10 terminals. Maximum 20 A fuse. Load 16 A max.

#10 wire - Use #10 terminals. Maximum 30 A fuse. Load 24 A max.

#8 and larger - Use die crimped lug type terminals. Use 1/4" or larger bolted connections. Calculate loads and length using ABYC tables. Normally larger wires are used near the engine to connect alternators, starters, inverters, etc. and should be grounded at the engine with a bolted connection.

Large load wiring for: anchor winches, water heaters, induction stoves, etc. should be carefully designed, and may require a separate large-load bus with bolted lug connections. Very long runs may require derating wire sizes.

Size fuses and breakers by the connected load up to the maximum allowed by the wire size. Examples: Lighting circuit draws 6 A -- Use #14 wire, fuse @ 10A. Pump draws 13 A -- Use #12 wire, fuse @ 15 A.

Following these basic guidelines will save both time and trouble. Suggested book for anyone doing their own wiring:

Boatowner's Illustrated Electrical Handbook, by Charlie Wing

If in doubt consult a qualified marine electrician.

[goboatingnow]

In metric that 1.5mm dia wire and m4 as a minimum. Won’t argue with that

[CharlieJ]

@Boatwright #48: Good advice with a couple of caveats; sizing the OCPD for a pump and sizing the conductor

>> Pump manufactures specify the OCPD size to ensure that the OCPD opens should a locked rotor event occur.

>> Size the conductor for the desired voltage drop under load then ensure that there is enough ampacity for the wire size.

Lighting circuit draws 6 A -- Use #14 wire, fuse @ 10A.

There is a functional relationship between the voltage drop caused by the wire and the current. As an example: If the example lighting circuit is 50' (25' to/25' return) here are the voltage drops and wire sizes:
3% drop; AWG 10
4% drop; AWG 12
5% drop; AWG 12
6% drop; AWG 12
7% drop; AWG 14
8% drop; AWG 14
9% drop; AWG 14
10% drop; AWG 16

[Shaneesprit]

Originally Posted by mitiempo

Oversizing a wire always makes sense, within reason. One size up from the Blue Seas (or similar) chart costs little. Wires should never get warm much less hot. If the wire gets warm in normal use it is too small for the load. One size up is not a problem as far as flexibility of wire is concerned.

Ampacity and practical use are very different. 10 awg 105 degree stranded copper has an ampacity of 60 amps according to Blue Seas. I would never use it for more than 30 amps intermittently and 20 amps continuous.

Note: Blue Seas busbars are 10/24, not 10/32.

ABYC allows up to 4 lugs on a post. I like to keep to 2 maximum.

Generally good advice
6mm or AWG10 is fine for 32A continuous, it’s my profession to test these things, in real world applications and over 32A and experienced it at 40A I need a derate of time on load so I wouldn’t get it tested in the first place. I have seen it done, but would have strong reservations. Say on a heater circuit where there is a time derate, in a practical sense, but it should never be applied, as heaters are always assumed to be continuous.. also seen a Din terminal rated for the load but connected by link bar to the next terminal where the link bar had burned.

[daveNZ]

Some recent comments are more helpful!
The dual Busbar I have actually does have 10/32 screws, I assume finer thread helps with torque. I was considering alternator output to this bus, as am fitting an external regulator to a 45A alternator, but I think I’ll put a bigger (than factory 4mm!) wire from alternator to starter +ve. It is 25mm from there to start battery, or maybe I’ll put it on the +ve bus post.
All small change compared to some of the users here, just my project boat! I’m hoping to reduce charging time from an hour or two per day. We use about 50+AHrs/day. I also have 175W Solar and Victron SmartReg. Cheers for the helpful hints.

[daveNZ]

Slightly different question.
Can I safely exceed (sum of all connections) the maximum busbar rating, if e.g. two high current connections are on the same stud?

i.e. I'm assuming here that most of the current between two connections, on the same stud, basically never go through the busbar, so don't count fully to the total current calculation.

Is that rubbish or reasonable?

[mitiempo]

Originally Posted by daveNZ

Slightly different question.
Can I safely exceed (sum of all connections) the maximum busbar rating, if e.g. two high current connections are on the same stud?

i.e. I'm assuming here that most of the current between two connections, on the same stud, basically never go through the busbar, so don't count fully to the total current calculation.

Is that rubbish or reasonable?

Yes, you can do that as the current does not pass through the busbar, only lug to lug.

[daveNZ]

thanks !! seemed logical but thought there may be something weird to take in to account.

[daveNZ]

Originally Posted by Boatwright

Never fail conservative rules of thumb:

Thanks, great notes which I've saved. Interestingly, tinned wire from local marine supplier has no insulation temp. rating, and staff say they are 'never' asked about it, in fact some have never heard of it!!!

[Boatwright]

Originally Posted by daveNZ

Thanks, great notes which I've saved. Interestingly, tinned wire from local marine supplier has no insulation temp. rating, and staff say they are 'never' asked about it, in fact some have never heard of it!!!

PVC insulation: 105 degs C (221 F)

If it gets that hot inside your boat the fiberglass resin is losing strength. Properly sized wire will never get anywhere near that warm.

[s/v Jedi]

I had to make a choice between a 4 stud 600A busbar or an 8 stud version. Pricey and space constraints made me try this out at ABYC maximum.

Even though this is within ABYC, I opted for the bigger busbar

[mitiempo]

Originally Posted by Boatwright

PVC insulation: 105 degs C (221 F)

Could be, or could be 60 degrees C. Hard to tell without a rating on the wire.

I would think that if it is good 105 C wire they would say so.

[s/v Jedi]

Originally Posted by mitiempo

Could be, or could be 60 degrees C. Hard to tell without a rating on the wire.

I would think that if it is good 105 C wire they would say so.

I think all pvc wire insulation is good up to 105C. It’s the property of the PVC, rather than the label that makes it so.