Does 5a/750v = 10a/375v?

[Tintin]

Just a quick question to get my head around something.

If some terminal (for example) or a switch have a max capacity rating of 5a/750v, does this mean it would also be OK at 10a/375v, or 20a/180v?

 

[Reverend Ludd]

I don't think so, what are you trying to do ?

 

[colhel]

amps x volts = watts. So I guess so

 

[sailorman]

amps x volts = watts. So I guess so

it may not cope with high amperage

 

[prv]

amps x volts = watts.

That is true, but switch rating isn't based on watts, so it doesn't work here.

Pete

 

[elton]

20 amps is 4 times 5 amps (obviously). If the switch has a resistance of (say) 1 ohm, then the power dissipation will be P = I ^2 R = 25 Watts at 5A and 400 Watts at 20A. In other words the power dissipation in the switch increases as the square of the current flowing through it.

I wonder if those who guess ever burn down houses.

 

[Reverend Ludd]

20 amps is 4 times 5 amps (obviously). If the switch has a resistance of (say) 1 ohm, then the power dissipation will be P = I ^2 R = 25 Watts at 5A and 400 Watts at 20A. In other words the power dissipation in the switch increases as the square of the current flowing through it.

I wonder if those who guess ever burn down houses.

That is an amazing answer.
You appear very clever without actually answering the question posed.

 

[peterb]

Just a quick question to get my head around something.

If some terminal (for example) or a switch have a max capacity rating of 5a/750v, does this mean it would also be OK at 10a/375v, or 20a/180v?

No.

The current rating (10A or 20A) is a measure of how much current the switch is able to carry and to break. It may also be constrained by the type of current (ac or dc) and by the type of load (resistive or inductive).

The voltage rating (180V or 375V) is a measure of the strength of the insulation in the switch.

So a rating of 10A/375V would mean that the system voltage must not exceed 375V, and that the current taken must not be greater than 10A. Dropping the voltage to 180V does not mean that you can use the switch to control 20A

 

[VicS]

I think you will find that the amps figure is the maximum current which the switch can safely carry.
Higher currents will require heavier conductors within the switch and heavier contacts.

The volts figure is the maximum voltage on which the switch can be safely used.

 

[elton]

That is an amazing answer.
You appear very clever without actually answering the question posed.

I can't say whether it's safe or not. I'm just pointing out the wrongability of some of the answers

 

[Tintin]

Thanks all. Much appreciated.

I reckon I'll be OK with 10a at 13.8vdc - whaddya fink?

 

[VicS]

Thanks all. Much appreciated.

I reckon I'll be OK with 10a at 13.8vdc - whaddya fink?

Now you have introduced something you did not mention earlier .... DC.

switch current ratings are usually very much lower for DC.

If its rated at 5amps/750 volts AC it is very unlikely to be suitable for 10 amps DC.

Get a switch that has the required DC rating.
e.g. An automotive switch from your local motor parts depot or even Halfords

Furneaux Riddall have a good selection

 

[david_bagshaw]

Just a quick question to get my head around something.

If some terminal (for example) or a switch have a max capacity rating of 5a/750v, does this mean it would also be OK at 10a/375v, or 20a/180v?

definately not. it would still be 5 A. think of it as the ampage determines the conductor size , & the voltage the quality & type of insulation.

DC switch gear often / generally has a swipe rub action to help keep the contact clean due to the sparking that occurs on separation, compared to AC

 

[maxi77]

Thanks all. Much appreciated.

I reckon I'll be OK with 10a at 13.8vdc - whaddya fink?

It will work, for a bit, and if you are lucky when it fails it will not cause a fire.

The current rating of switches is the limit, changing the voltage does nothing for you, and many stiches are derated for DC because of arcing on the contacts.

 

[mitiempo]

It depends very much on the switch.

The one below is rated for 10 amps@ 250 volts and 15 amps @125 volts AC, but only for 15 amps @ 12 volts DC. As noted previously DC ratings are lower.

 

[nigelmercier]

The switch is rated UP TO 5A, and UP TO 750V AC.

Any other combinations are not within limits, and for DC you would have to de-rate it, even at 12V.

Just in case that isn't clear: the answer is no, you cannot use it for your purpose. I'm making a point here because you seem to have read the early replies, then chosen to believe only those that let you use the unsuitable switch.

Reminds me to listen to more weather forecasts, so I get a better choice