Dangers of swapping negative and positive on a wastewater pump?

[Thomas C King]

Thanks all, I think we've solved it. We connected the Whale Gulper to the circuit, which includes the switch, and it worked fine this time. So, to summarise with a timeline:

 

1) First switching on the old pump made the circuit breaker trip.

2) Swapping the circuit breaker did not help

3) Then, swapping the old pump for the Whale Gulper blew the Whale Gulper's included in-line fuse, and still made the circuit breaker trip.

4) Replacing half of the wiring, probably the negative (albeit with red wire, sure that's not going to ruin anyone's day), did not stop the old pump from tripping the circuit breaker.#

5) Swapping the circuit breaker again got some action out of the old pump but after a few seconds of a glowing wire, the circuit breaker tripped.

6) But then swapping the old pump for the whale gulper, on the half-replaced circuit, with the new circuit breaker, seemed to work.

 

Not sure what conclusions I can draw. But now to plumb it in, somehow.

Edited May 17, 2020 by Thomas C King

[Jen-in-Wellies]

2 minutes ago, Thomas C King said:

but after a few seconds of a glowing wire

Glowing wire? Could you elaborate? At first reading that sounds very not good. What size wire is being used?

Jen

[Thomas C King]

3 minutes ago, Jen-in-Wellies said:

Glowing wire? Could you elaborate? At first reading that sounds very not good. What size wire is being used?

Jen

Thicker than the original ones. 2.5mm I think.

[Jen-in-Wellies]

8 minutes ago, Thomas C King said:

Thicker than the original ones. 2.5mm I think.

And the glowing wire? The breakers are supposed to protect the wires from overheating. What size breakers are you using?

Is that 2.5mm diameter, or mm² cross sectional area of conductor?

Edited May 17, 2020 by Jen-in-Wellies

[Thomas C King]

1 minute ago, Jen-in-Wellies said:

And the glowing wire? The breakers are supposed to protect the wires from overheating. What size breakers are you using?

I don't know, but I'll investigate because I've been swapping round the circuit breakers willy-nilly. By glowing wire I mean the point of contact between the pump's wire and the boat's wire(s). I actually can't remember whether it was the old wire or the new wire that we've just started using for one half of the circuit.

[Jen-in-Wellies]

It sounds a bit melodramatic, but 12V wiring overheating because the fuses, or breakers are the wrong size to protect it, or bypassed can lead to a fire that can burn a boat out in only a few minutes. Just because the voltage isn't high enough to give a shock doesn't mean it isn't to be treated with respect.

Jen

[cuthound]

10 hours ago, Jen-in-Wellies said:

And the glowing wire? The breakers are supposed to protect the wires from overheating. What size breakers are you using?

Is that 2.5mm diameter, or mm² cross sectional area of conductor?

 

Worrying because even 1 mm square cable is rated at 14 amps. Would need a lot more current than that to make it glow.

 

OP needs to ascertain all cable sizes and ensure they are protected by suitably rated breakers or fuses.

 

Sounds like the old pump had a short circuit. 

[Mad Harold]

11 hours ago, Jen-in-Wellies said:

And the glowing wire? The breakers are supposed to protect the wires from overheating. What size breakers are you using?

Is that 2.5mm diameter, or mm² cross sectional area of conductor?

Sounds like somewhere in the circuit the current is running to earth.

The cicuit breaker should trip when this happens.

 

[ditchcrawler]

15 hours ago, Thomas C King said:

I By glowing wire I mean the point of contact between the pump's wire and the boat's wire(s).  

Note this point, it could just be a bad connection and not a short

[cuthound]

2 hours ago, ditchcrawler said:

Note this point, it could just be a bad connection and not a short

 

Usually a HR joint will damage the insulation (discolouration, brittleness) well before the conductors begin to glow.

 

What did the insulation look like when tne OP first looked at thev pump and again after he noticed the cable glowing?

Edited May 18, 2020 by cuthound
To add the last paragraph