Wiring for macerator toilet

[Farey]

Hi

 

I've ordered a 60' narrowboat sailaway, which I should take delivery of later this month and am planning on fitting out myself. I've been reading up on the electrical installation, and have a question.

 

I'm planning on putting in Vetus macerator toilets, which the catalogue states have a 400W motor and should draw 32A using a 12V supply. If the toilet is halfway along the boat, this gives a cable run of about 20m. Doing a calculation of voltage drop, I get a drop of 1V if I use 10mm^2 cable. This seems a) too high a drop and b ) pretty thick cable. The Vetus installation manual on the web suggests using 2.5mm^2 cable for connecting to the toilet.

 

So, my question is, what is the correct size cable to use? Does the fact that the pump is only running for a few seconds during a flush mean that smaller sized cable can be used? It seems that whatever I do its probably best to give the toilets their own circuit?

 

Chris Farey

Edited June 2, 2005 by Farey

[stuart]

I would use a seperate fuse/cable run to both toilets. The last thing you want is a fuse blowing and you cannot use either toilet until you get the fuse replaced - odds on you won't have the correct spare when you need it!

[dor]

The short time the pump is running means you can undersize the cable as far as it overheating is concerned, but you will still get the volt drop.

 

I would expect the volt drop to be very significant over that distance and that current, so your figures are likely to be correct.

 

There are tables around giving voltage drops, or just put the figures in the standard formula.

 

10mm^2 cable doesn't seem too big to me. Most people would recommend that thickness for a fridge, let alone something drawing 32A

[Richard Bustens]

The cable that comes on the toilet is only 4mm i make the calculations for one at 20mtr 33.3 amps and a volt drop of 1.87 at 6 mm and 1.12 on 10 mm i used 6mm but am 24v. 10mm cable is not that big it should be ok to use that

[Farey]

10mm cable is not that big it should be ok to use that

21527[/snapback]

 

Of course you're right - 10mm^2 isn't that big, and maybe I should consider bigger. Thanks for the answers.

 

Chris Farey

[Richard Bustens]

I dont think you need to go bigger Chris, it will only run for 5 or 10 secs, i can not make my mind up if you have one or two toilets, but if two i think i would run separate wiring to both as Stuart says, though they should not be both used at once very often.

Edited June 2, 2005 by Richard Bustens

[Gary Peacock]

Why not save money and use a 240v one?

 

Gary

[John Orentas]

Chris.

 

I too make it one volt drop, that's ok for a motor, always remember that the manufacturer will always give you a "maximum" figure.

The running duration is not really important there will be no appreciable heating of the cables unless you really go to extremes.

Use a fuse well above the 32 amp figure, about 50 or 60 amps.

[DHutch]

Why not save money and use a 240v one?

- lol

[Richard Bustens]

Why is it off topic Dan?

Vetus make a 240v one but it is no cheeper, also there are a full range of domestic units that will use a ordenary toilet from B&Q etc but the water usage is large and also the pipe requires to go to the tank is bigger also the maserator box is a big lump.