Forward and Aft Johnson Bilge Pump Fuses

[dbsea]

Can someone confirm that these should be 5A fuses for the Johnson pump / electric float sensor combo? All the documentation I can find points to yes that they should be, but for some reason my fuse panel had 15A fuses in for these. I swapped them out for 5A but would like to confirm. Thanks!

 

[fishheadbarandgrill]

on my 2011 R29, same pump/switch, they are 5A.

 

[NSM]

Our 2022 29 manual shows 7.5 amps. I’m not at the boat to confirm what’s actually in the fuse block.

Cheers
Scott

 

[dbsea]

Thanks both. Scott, I think you have the newer rule auto pump vs the older Johnson style, and the rule ones might use a different fuse.

 

[Maggie Anne]

I have 5 amp fuses in my boat but should say that I've had to replace them several times as it seems when heavy rain gets a lot of water in the bilge and they have to work for longer periods the fuses blow. I was thinking of replacing them with a slightly larger size, say 7.5 amp?

 

[dbsea]

I have 5 amp fuses in my boat but should say that I've had to replace them several times as it seems when heavy rain gets a lot of water in the bilge and they have to work for longer periods the fuses blow. I was thinking of replacing them with a slightly larger size, say 7.5 amp?

It would depend on what the AWG of the conductor is. 14AWG can only handle 5.9A. I am not sure what the gauge of the bilge pump wiring is. 12AWG can handle 9.3A, 10 can handle up to 15A. If you oversize the fuse you risk heating the conductor or the pump housing up, and possibly melting it down, defeating the purpose of the fuse.

 

[Maggie Anne]

Thanks Dave, I will check the wire gauge.

 

[dbsea]

Thanks Dave, I will check the wire gauge.

It looks like its 16AWG wire according to the wiring diagrams for both RT and CW boats. That means the max current is 3.7A. The Johnson pump is 12V 3A and calls for a 5A fuse.

 

[Katmat]

Capacity Chart
This chart is a simple "max capacity" chart for a short wire run. Increase the wire size for long runs - for example the wires running to the back of a vehicle to power the taillights may need to be one size larger to account for the length.

Gauge 110V 12V
22 5A 5A
20 7.5A 8A
18 10A 10A
16 13A 20A
14 17A 40A
12 23A 60A
10 33A 100A
8 46A 150A
6 60A ??A
4 80A ??A
2 100A ??A
1 125A ??A
0 150A ??A

 

[HawaiianFish]

DBsea, I just went down this rabbit hole. My 2019 C30 Rule bilge pump uses 7.5 amp fuses found in the 1/4 berth (cave) run though the Thruster battery for 24/7 operation. Johnson use 5 amp. I got this most recently from As the Prop Turns, Spring Commissioning Part 1 @ 35:15 in the video on YouTube.

The literature I found in my boat confirmed the use of 7.5amp fuses for the Rule.

 

[Gin]

This links to an online ABYC-based calculator to determine the right wire gauge for a particular ampacity or, alternatively, the maximum ampacity for a particular wire gauge. https://boathowto.com/electrics/wire-size-calculators/

Nigel Caldor recommended it in his solar power presentation this year at the Seattle Boat Show. Perhaps to promote the “Boat How To” course he is associated with. The online calculator, unlike the course, is free. A printable table is on the same website here: https://boathowto.com/electrics/abyc-ampacity-tables/

Gini

 

[dbsea]

Interesting, thanks Gini. I'm not sure why that is so different from what i was referrring to, which is the AWG wire gauge chart? I must be missing something..

https://www.powerstream.com/Wire_Size.htm

 

[Gin]

I’m not sure of the answer to your question, Dave. My hunch is that the “American Wire Gauge” standard you linked to is for use in as a general standard in the US, while the ABYC standard is specific to marine wiring. But that’s just my instinctive thought. Others on the forum probably have an answer for you.

For anyone interested, I did discover a reasonably good BoatUS article on calculating wire size for both AC and DC boat systems. It recommends a $4.99 phone app that ABYC has developed. The Nigel Caldor calculator seems to do the same thing for free. But the app could be helpful for anyone working on their boat without an internet connection.

The BoatUS article is here: https://www.boatus.com/expert-advic...ve/2020/february/choose-the-correct-wire-size

Gini

 

[CruisingElvinRay]

Blue sea has a great app that will calculate the cable or fuse size for you based on actual round trip lengths and power requirements.

https://apps.apple.com/us/app/circuit-w ... d576865083


Sent from my iPhone using Tapatalk

 

[knotflying]

I have 5 amp fuses in my boat but should say that I've had to replace them several times as it seems when heavy rain gets a lot of water in the bilge and they have to work for longer periods the fuses blow. I was thinking of replacing them with a slightly larger size, say 7.5 amp?

It would depend on what the AWG of the conductor is. 14AWG can only handle 5.9A. I am not sure what the gauge of the bilge pump wiring is. 12AWG can handle 9.3A, 10 can handle up to 15A. If you oversize the fuse you risk heating the conductor or the pump housing up, and possibly melting it down, defeating the purpose of the fuse.

I think you should recheck the chart you may have used for wire size and amperage. As an example 12 gauge is rated for 20 amps.