Shower pump switch

[jddevel]

Will a 240volt isolating switch be O.K as a 12volt shower pump control switch please?

[Ex Brummie]

Mine has lasted 30 years, so I would say yes.

[Scholar Gypsy]

It's the current rating that matters really, not the voltage. So a lighting switch (say 2A) not really up to it, but a power circuit switch (20A plus) should be.

[Tony Brooks]

22 minutes ago, Scholar Gypsy said:

It's the current rating that matters really, not the voltage. So a lighting switch (say 2A) not really up to it, but a power circuit switch (20A plus) should be.

No its not. The contact design is also important for 12v DC switches. AC current turns itself off every 100th of a second so extinguishing any tendency to arc. DC keeps going and may burn/weld contacts designed for AC that are generally smaller. Having said that we know many people use AC switches for DC without many problems but I would use a high current AC switch in preference to a low current one. I think many pumps require a 10 amp fuse so I would go for a 20 amp (minimum) AC switch and hope the contacts last. I suspect one from a quality manufacturer may do a better job than a nominally DC switch from Ebay and the like.

[jddevel]

My reason for this question is that I`m finding it difficult in locating a suitable source for DC components other than via adverts on the internet with no real proof of quality. The major players I`m familiar with are in the domestic market or local car factors. Is there any guarantee that online chandlers will supply the right item without grossly overcharging as some comments on the forum seem to imply. Any suggestions please for good quality sources.

[Alan de Enfield]

28 minutes ago, jddevel said:

Any suggestions please for good quality sources.

ASAP Supplies

https://www.asap-supplies.com/

or

 

http://www.12voltplanet.co.uk/

Pay what is needed to get proper 'marine' fittings.

The number of people who jeopardize their £100,000 boat to save two-pence on a switch...............

 

For want of a nail the shoe was lost.
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the battle was lost.
For want of a battle the kingdom was lost.
And all for the want of a horseshoe nail.

[Chewbacka]

It's all about risk and consequence etc.  So a 32A or 45A cooker type switch for a water pump is probably going to last.  If it is only an isolation switch, rather than an on/off operation switch then it is rare, if ever, that it will switch off under load, so will not suffer any arcing or other concern, so will last forever.  That said I would not use a 240V AC switch for a solar panel as the contact gap may not be enough to quickly snub out the acr at the higher voltages.  As to consequence, if your switch becomes a bit unreliable then you will have water supply problems which will not sink the boat or harm anyone, so it's up to you to decide how serious a water pump failure is.

[Alan de Enfield]

3 minutes ago, Chewbacka said:

If it is only an isolation switch, rather than an on/off operation

My impression was that it is to be used as the "on/off" switch.

 

11 hours ago, jddevel said:

.....as a 12volt shower pump control switch please......

I guess that shows the importance of correct terminology.

[Chewbacka]

Just now, Alan de Enfield said:

My impression was that it is to be used as the "on/off" switch.

 

I guess that shows the importance of correct terminology.

You are probably right, when I first read it I thought the op meant the shower supply pump, but thinking about it, it is more probably the whale gulper or similar used to empty it. More the importance of not making assumptions.

[Tony Brooks]

The OP PMd me to ask if he could use a 45 amp cooker switch. All I can do is refer him to Chewbacka's answer above ans my explanation as to why using AC switches for DC loads is not best practice.

The shower switch will be turned off under load and to make matters worse its an inductive load the will cause a short duration voltage surge making arcing more likely.

If the switch contacts welded together its no big deal as long as the cable is the correct size. the pump will keep running so the fuse will have to be pulled out or the circuit breaker tripped pending switch replacement. If the contacts just burned so they no longer make contact then you just smell or a wile until the switch is replaced. I do not see either as a danger, just an incontinence.

MY guess is that a 13 amp switched spur would probably do the job for a while but how long that while is no one knows. Given what the OP has I suspect I would try tofind a higher rated switch but I can not say it is OK to fit an AC switch to a DC circuit.

[Alan de Enfield]

3 minutes ago, Tony Brooks said:

..........just an incontinence

How many folks 'pee in the shower' ?

[Alan de Enfield]

4 minutes ago, Tony Brooks said:

I can not say it is OK to fit an AC switch to a DC circuit.

I would repeat - why spend your life savings on a boat and cut corners by using an incorrect item that is (maybe) £1 saving.

Failure of the switch may not cause your boat to sink, but, the inconvenience of having a 'welded closed' switch and having to then find a (correct) 12v replacement just does not 'stack up for me'

Do it 'right' and do it once !!!

[bizzard]

A massive DC knife switch would be ideal, with an enormous two handed handle to operate it. Like you see on horror films when someone cuts off all the electric lights in the haunted house.

[Tony Brooks]

11 minutes ago, bizzard said:

A massive DC knife switch would be ideal, with an enormous two handed handle to operate it. Like you see on horror films when someone cuts off all the electric lights in the haunted house.

I bet the visible arc would make them jump a bit - like it.

[Scholar Gypsy]

..

16 minutes ago, bizzard said:

A massive DC knife switch would be ideal, with an enormous two handed handle to operate it. Like you see on horror films when someone cuts off all the electric lights in the haunted house.

and would deal with any surplus methane from the toilet.

[Chewbacka]

Actually a big switch is not the best way to go, rather it would be better to use a small neat switch the op likes and use that to switch a DC relay to switch the pump on and off.  If the op really wants to use an AC switch to directly switch the pump on and off, then to quench the back emf as Tony raises as a concern - which it is - then you could put a chunky (say 5A) diode across the switch contacts (obviously reversed biased).

[jddevel]

Ok I accept the necessity to use the correct switch. What I was trying to solve was the fact that a opening has been cut in the panelling to accommodate a 240 volt size pattress -the sort used in stud walls in houses. I`ve either got to try and patch the hole which obviously would be a shame or try and find a 12volt switch that fits the pattress that was/is going to be used. For clarification it is the switch located in the bathroom that switches the Whale Gulper on when the shower is in use. Does anyone know of a 12volt switch that will fit the pattress described please. Or at least link me to the normal 12 volt switch to be used for the shower purpose. I must admit that all of this was getting ready for the marine electrician and my cutout was designed on the experience of the switches I`ve used in the boats I`ve hired over the years. Admittedly some you had to press and hold to empty but to my recollection they were all sort of domestic light switch physical size.

[Tony Brooks]

Get a pattress blanking plate (like a switch but with no gubbins mounted on it) and drill it to accept whatever 12V switch you choose.

[b0atman]

12 hours ago, Ex Brummie said:

Mine has lasted 30 years, so I would say yes.

my architrive light switch is getting on for 20 years old probably 5amp rated but does the job 

[cuthound]

1 hour ago, bizzard said:

A massive DC knife switch would be ideal, with an enormous two handed handle to operate it. Like you see on horror films when someone cuts off all the electric lights in the haunted house.

When I first started work, one of the buildings had 1600 amp, 50 volt DC generators (AC motor driving a DC generator) to charge the batteries and 600 amp ones to meet the normal load.

There was a DC switchboard with several of the type of knife switches you describe. They had sprung edges, to break the load circuit quickly, and thus avoid drawing too big an arc.

[Tony Brooks]

42 minutes ago, b0atman said:

my architrive light switch is getting on for 20 years old probably 5amp rated but does the job 

Yes, but that is for lights that are not an inductive load so no voltage surge on switching off. Actually a florescent probably is an inductive load but with nowhere near the inductance of a motor. Also lights tend to be low power devices, unlike motors.

No one said he can not use household switches, just that it is not good practice.

Edited May 10, 2017 by Tony Brooks

[smileypete]

For a gulper with 5A fuse rating, just use a standard patress light switch which will have a positive switching action, job done.

I estimate the risk of failure for the above setup to be between 2 and 5% long term, probably mostly due to manufacturing defect, make of that what you will.

We're talking a normal narrowboat here, not a megayacht. If the switch fails in 30 years (VERY unlikely) just go to screwfix and get another.

Look instead for *common* electrical failure points on boats, these are often crimp connections which can benefit from some OCD like attention to detail...

Edited May 10, 2017 by smileypete

[smileypete]

55 minutes ago, cuthound said:

When I first started work, one of the buildings had 1600 amp, 50 volt DC generators (AC motor driving a DC generator) to charge the batteries and 600 amp ones to meet the normal load.

There was a DC switchboard with several of the type of knife switches you describe. They had sprung edges, to break the load circuit quickly, and thus avoid drawing too big an arc.

Some of the inexpensive solar specific DC switches are just a normal AC three phase switch with contacts wired in series, the arc is then spread across three contacts instead of one. Cheap way of boosting the overall DC contact rating.

Edited May 10, 2017 by smileypete

[OldGoat]

How to make a meal over a simple application.

IME a simple toggle switch will do the job this one here -

http://cpc.farnell.com/apem/641h-2/15a-toggle-metal-dpst-on-off/dp/SW02432

States it'll do 15A at 12V - se the technical specification. Order two and you'll get free postage

(10 years later when the original hasn't broken you'll be able to sell it on eBay)

[Ssscrudddy]

I'm confused now, some are saying don't use a 240V switch while another says it's ok.
I too have a whale gulper for my shower waste pump. I wired it up with a bog standard light switch from Screwfix. So is this ok or not?