Really dumb question!!

[dunny]

If you have a light switch rated at 6amps and a ringmain (or ring final as I have learned on this forum!!) rated at 32 amps and you use the ringmain to supply power to the switch would everything be OK until something on the ringmain drew more than 6amps?

Not an important question and not something I am thinking of doing but reading all the posts on this forum from the most knowlegeable contributors I think I am beginning to understand more. Are amps like a measure of the flow of a specfic voltage charge?

 

[Spark123]

Don't quite get what you are asking, but you would NEVER connect a standard 6A light switch directly to a 32A ring main or any other circuit fused above 6A unless it is fused down (via 5A FSU for example).

 

[dunny]

No I understand that, I was asking the question as I was just trying to understand what makes a ringmain 32a and a lighting circuit 6amps.I am not doing any work on anything related.

Better question I guess would have been to say what exactly are amps?

Presumably the voltage of the supply to the lighting circuit and the socket circuit are the same with only the things connected to the circuits that draw current and increase the amps?

 

[Damocles]

You would be correct in saying that the things connected to the circuit determine how much current is drawn. However, the maximum is limited by a fuse or breaker which automatically disconnects when the limit is reached. So a 6A breaker is one designed to allow 6A to flow but to trip out if the current goes much above this. Equipment is normally described by the rating at which it is designed to work. So a 6A circuit is designed to work at 6A, a 32A one at 32A. You should not use equipment designed for a lower rating on a circuit with a higher rating.

 

[Spark123]

Better question I guess would have been to say what exactly are amps?

Amp (ampere) is the SI unit for current flow. See Encylopedia

Presumably the voltage of the supply to the lighting circuit and the socket circuit are the same with only the things connected to the circuits that draw current and increase the amps?

The voltage supply is normally the same for all circuits in a CU, nominally 230v. Each item connected to a circuit will draw current and increase the load on that particular circuit by whatever the loading of that device is (amps) i.e. the loads add up.

 

[dunny]

Thats what i thought - isnt it quite easy then to put too much load on a socket circuit just by having appliances plugged in?

I guess most appliances only draw a small amount of amps?

Do sockets themselves draw any current?

Not wanting to waste your time with my simple questions but you guys have so much knowledge of this stuff seems a shame to not to ask....

 

[Damocles]

No, If you did overload it you would trip a breaker or fuse. This does not often happen, so experience says it is not so easy. 32A is generally enough for what one person or family is likely to want to plug in at one time. A bigger house or more recently wired may have two or three rings.

 

[Spark123]

Thats what i thought - isnt it quite easy then to put too much load on a socket circuit just by having appliances plugged in?

You can easily overload a ring main by plugging in too many high current appliances. A ring main is designed so it should only serve an area of maximum 100m². The appliances which would normally be used in that particular area may also be taken into account.

I guess most appliances only draw a small amount of amps?

Yes, table lamps, VCR, satellite decoder etc draw a relatively small amount of current. Items such as heaters and kettles draw relatively large amounts of current.

Do sockets themselves draw any current?

No, with the exception of sockets with an integral neon indicator which takes a few mA (1mA = 1000th of an amp).

 

[dunny]

Thnaks. The mist is beginning to clear....

 

[kendor]

each item connected to a circuit has a value of resistance(super conductors the exception) and as these resistances are connected in parallel then Ohm's law states that resistances in parallel give a total value less than the lowest resistance connected and as resistance has an effect on the current flowing in the circuit(it's name suggests resistance to current flow) the lower the resistance the higher the current as a bit of further info, the voltage is equal across the parallel loads although this voltage can fluctuate dependant on load and the ability of the source to supply the needs of the load applied.

 

[BenStiller]

Kendor, you really cleared it up for him with that reply

 

[kendor]

thanks i like to help

 

[dunny]

So when looking at a specific appliance I see mention of its voltage and wattage but no reference to how much current it would draw. I guess this is because unless its quite a powerful appliance (maybe like an electric fire) the current it draws is negligible?

It doesnt seem very easy to know whether your connected appliances would exceed the maximum for the breaker. But I suppose as Damocles said its not common unless you go a bit OTT with the amount of things you try to run off a single ring.

 

[Spark123]

Appliances usually have either a watt or a VA rating. Amps x volts = VA.
Volts x amps x power factor(pf) = watts. In items which are resistive such as filament lamps, the pf is 1 and hence volts x amps x 1 = watts. Other items such as motors or fluorescent lamps (inductive loads) have a lower pf and hence it is not as straightforward to calculate.

 

[Adam_151]

Sometimes the amps are not marked on an applience, because they can be calculated.

Power (watts) = I (amps) x v (volts)

If you rearange this you can see that I(amps) can be worked out by power (watts) divided by volts

Power is a measure of transfer of energy (one watt = one joule a second)
Current is a measure of flow of charge (one amp = one coulumb per second)
Voltage is a measure of energy per coulumb (one volt = one joule per coulumb)

If you look at the above definations and at the P=IV equation, it might help you to understand it a bit better

Hope this is helpful

Adam