Do I need to re-wire my toilet...?

[Karel]

I took my Carver in to a boatyard up the Thames recently (I won't say who it was because there's some legal stuff going on now

) to have several jobs done. Some of them are now a complete dog's dinner.

One was the fitting of an electric toilet - <u>a Vetus WCS</u>. It seems to have been wired completely wrong.

The manual syas that the power requirement at 12V is 35A, the wiring should have a minimum cross section of 6mm(squared) (AWG8) @ 12V, and the fuse rating is 30A @ 12V 'medium time lag'.

The technician seems to have used wiring of about 10amps (I've no idea what the cross sectional area of that is!) and used a fuse rated at 20A.

As could be expected, the fuse blew /forums/images/graemlins/frown.gif . I am now in a major (like, very major) row with the boatyard, and have to decided to put right the work myself rather than live without a functioning head for the season.

I'd like to know if all the wiring needs replacing /forums/images/graemlins/crazy.gif and if anyone knows where on-line I can order the correct 30A fuse and a good fuse holder - the guys at Wholesale Fittings were completely thrown by my questions.

What should I look out for when ordering the fuse? RS components don't seem to specify what voltage they are used at, so am I right in thinking that a domestic ring-main 30A fuse is the kind of thing I should be looking at? This surprises me. If that is the case, the wiring really does need a drastic upgrade... /forums/images/graemlins/frown.gif

Many thanks for any help.


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[Phoenix of Hamble]

can't hlp with much of it.... but a domestic 30A fuse is rated at 240V, not 12V, so would be significantly oversized.... remember V=IR....with a voltage of 20X smaller than rated, it would need 600A to blow!

 

[philip_stevens]

have a look at Index Marine for circuit breakers, fuses and cable (that url for the index).

 

[PBooth]

Hi,

A 30 amp fuse is just that, at any voltage. So you just need to order whatever amperage is specified and size your cable to suit the rating of your toilet and allow for volt drop for the length of the wiring. I would recommend using 'maxi blade' type fuses, available at auto electrical stockists, RS, CPC etc.

Peter

 

[boatbuilder]

6MMsq is ok for about 40 amps, but it depends on the length of the cable. remember to measure the cable in both directions.
Look at a company called asap-supplies.com. very helpfull and quick deliveries.
I am trying to type faster honest!!!
Good luck

 

[nigelhudson]

Contrary to what the other post says fuses are not voltage specific - 30amps is 30amps irrespective of the voltage. However fuse holders are voltage-rated because of the degree of insulation required and fuses are designed to match the holder.
You can buy automotive type fuses (two spade connectors in line encapsulated in plastic) as found in your car fuse box. To match these you can buy in-line holders that can be crimped to the cable. I have this arrangement to connect my inverter to one of the service batteries. I suggest that you try an automotive electrical supplier.

 

[Karel]

Thanks for all the info. I'm checking out the links now,

So, if I've got this right, any fuse rated at 30A will do the trick (but what about the 'medium time lag' bit? Is that just a normal fuse?) and the wiring should be heavy duty 30-40A? Even for only 6 seconds of operation?

 

[Karel]

Ah, just saw your post Nigel. Thanks.

 

[misterg]

[ QUOTE ]
domestic 30A fuse is rated at 240V, not 12V, so would be significantly oversized.... remember V=IR....with a voltage of 20X smaller than rated, it would need 600A to blow!

[/ QUOTE ]

Sorry, but this is carp (anag.) /forums/images/graemlins/smile.gif It will still blow at (nominally) 30A, whether 12V or 240V, but it still isn't really the right thing to use, as domestic mains stuff is rated for AC, not DC. DC needs much meatier design.

Karel - if you are familiar with RS, have a look at 405-9214, which I imagine would be the sort of thing you would use;

BUT:

Your boat must already have some similar fuses, or circuit breakers for the other circuits - why not get the same?

BIG BUT : (no not personal, honest!)

/forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gifDon't uprate the fuse without uprating the wiring /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif<--- IMPORTANT

The fuse is there to stop the wire setting fire to your boat. Make sure the wire can take the current the bog needs (current rating, and voltage drop). Then make sure the fuse is rated to protect the wire.

Andy

Edit: B*gger! must learn to type faster - only one reply when I started typing! /forums/images/graemlins/blush.gif

 

[Karel]

I'll look that RS item up.

Yes, will certainly upgrade the wiring.

The current fuses etc date from 1982...!

Any thoughts on using the E3340 circuit breaker here? Are these things reliable?

Man, I am so pissed off with this boatyard! I'd love to name them, but that wouldn't be wise.

 

[Karel]

Hey! That RS item is virtually the same as the breaker i found at Index marine.

How very amusing...

 

[Guest]

Something is very odd here: I have just read the manual, on line, and it says minimum wire size is 2.5 mm2 (AWG14)! Then goes on to state it takes 32A.

That does not include the input pump if you have one. Ignoring the fact that 2.5mm2 is too small there is no mention of fuse sizing or wire sizing due to length of runs.

Obviously you do not have the same manual as the one online.

Assuming you are talking about the supply distribution fuse and not the optional inlet pump fuse this can not be changed until the wiring issue is resolved. If it is the inlet pump fuse then that should be sized to blow if the inlet pump stalls and is not part of the toilet specifications as such.

Questions:
1. Do you have an inlet water pump added?
2. Is it close to the toilet?
3. What is the wire size from the distribution panel to the toilet?
4. What is the size of the fuse near the distribution panel?
5. What are the distances?

As a comparison: Lewmar's Anchorman uses a 700W motor. For a 15m installation (~7.5m battery to motor distance) they recommend 25mm2 (4AWG) wire. For just the switch relay wire they recommend 1.5mm2 (14AWG).

I know the duty cycles are different. But for just under twice the current Lewmar are recommending 10 times the wire size?

Could it be the case that the installer has used the on line manual to get the minimum wire size and then when selecting the fuse he has sensibly not fitted the 32A on such a tiny wire. Not an excuse just a possible explanation.

 

[VicS]

I agree the statement about needing 600amps to blow the fuse is total garbage but a word of caution.
I think I am right in saying that a domestic fuse (which might be described as 240 volt) will carry the rated current without blowing indefinitely and will require an overload to blow it. An automotive fuse (which might be described as 12volt) is designed to blow at the stated current.

 

[Karel]

Intriguiging what you say Vic, but then if a 30A domestic fuse is meant to carry 30A, when does it blow? At 31A?

And if the 'installation instructions' I have here say that the current is 35A (albeit for only 6 seconds) then why is the fuse rated to blow at 30A?

Solar, you have now got me seriously worried. /forums/images/graemlins/grin.gif

I believe the installer worked from the very installation instructions leaflet I have in my possesion. But then that makes even less sense...

To his credit, the plumbing looks sound, but I've yet to find the two cut-off valves this booklet says should be installed... /forums/images/graemlins/frown.gif

1. Do you have an inlet water pump added?
Not as far as I know. I think the system takes water from the regular pressurised water supply on the boat.

2. Is it close to the toilet?
Not particularly... 4ft.? But it's of reasonably high pressure

3. What is the wire size from the distribution panel to the toilet?
It's about the same thickness as you'd find in a domestic 13A cable.

4. What is the size of the fuse near the distribution panel?
5. What are the distances?
There is a cable run to the distribution panel of about 8 ft. including a diversion for the only fuse rated at 20A. There are a couple of breaks in this wire that are re-connected using regular domestic plastic connector strips (I suspect that's not good enough either). I've yet to investigate what exactly happens inside the distribution panel...

/forums/images/graemlins/crazy.gif

 

[misterg]

VicS - you may well be right. All I know is that the whole business of the protection characteristics of fuses / circuit breakers is a too large a can of worms to be described by a simple amps rating.

I've seen these circuit breakers used, but don't know how reliable they are (I would assume they are OK). Thermal or thermal/magnetic would be better suited to the "slow blow" requirement - magnetic only is least suited, but may well be OK.

(Part no. for 30 amp version is 405-9208. Part no. for 35A posted previously)

Extent of knowlege reached!

Andy

 

[tome]

Blimey, youre in danger of over complicating

As a rule of thumb, you should never drop more than about 0.5 Volts on your cables

So need 2 people. One to operate bog, other to take measurements using voltmeter

Initially put voltmetre on supply battery and have assistant operate bog. Measure voltage 1 whilst bog operating

Next go to bog and put meter across terminals. Have assistant operate it again then measure volts again. Voltage 2

As long as V1 > V2 + 0.5V add cable

 

[ningcompoop]

Sorry about your loo Karel and I do hope you get it sorted quickly and easily! I was just wondering about the figures regarding 12v/240v fuse equivalance - I just reckonned out that a 240v 30amp fuse would take an energy throughput of 7200 watts before blowing, and again came up with misterg's figure that at 12v the current would have to be 600amps to produce the same amount of energy, and surely its this energy that causes the fuse to blow.The figure does some a tad excessive, but what am I missing here? I have got an O-level in physics, but that was 23 years ago! Have I mislaid some of my marbles?

 

[Karel]

I always find that bit of electrickery completely mind-bending too.

Good idea tome - measure it!. Thing is, I want to get it going by the weekend, and am not there again till Thursday.

Now here's a question about circuit breakers; some specify "combined breaker/switch" What does that mean?

 

[tome]

Ok, so you have a cable run of 8 ft and a current load of 30A or thereabaouts

Means your total run there and back 16ft say 5m

Max drop is 0.5V so you need #14 wire which is 2mm sq diameter with a continuous cable run - no joins

 

[Karel]

So why does it say here "use wires with a minimum cross-section of 6mm(squared)"?