watts to amps

[OhmSafe]

hi all just a quick one am i right in doing this..

3000w / 230 = 13amps?

 

[ricicle]

Yes.

P = V x I
I = P / V
V = P / I

 

[ban-all-sheds]

hi all just a quick one am i right in doing this..

3000w / 230 = 13amps?

If the load is rated at 3000W at 230V, yes.

If it's at a different voltage then no.

 

[OhmSafe]

its just i have a 16amp radial and was working out a plug in heater and a kettle and was getting 17amps thats over loading with just them two items?

 

[MalcofArabia]

Yes but your heater will have a thermostat and will be cutting in and out. You will use your kettle for short bursts of 5 minutes unless you going to fill a bath up, but even then it will switch of when boiled.

So in the advent of perhaps bot heater and kettle being on full blast at the same time and producing that 17amps, your protection will be able to withstand an overcurrent of 1amp for those few minutes.

It's called diversity.

 

[OhmSafe]

yeah for them 2 items but if you have boiler, tvs and dvds on ect... aswel as the heater and kettle

 

[bernardgreen]

P = V x I
I = P / V
V = P / I

V = R x I

R = V / I

But resistance R is the only constant ( well almost constant ) value in heaters and similar equipment

A heater rated as 3000 watts at 230 volts is 13 amps and therefore has a resistance of 17.69 ohms at operating temperature.

The same device at 240 volts will take 13.56 amps

and at 253 volts 14.3 amps ( 253 = 230 plus 10% which is possible in UK networks ) which means the 3000 watt device is taking 3618 watts.

 

[ban-all-sheds]

So now it's a 16A radial with a plug in heater, a kettle, a boiler, TVs, DVDs etc?

Anything else?

Assuming the circuit was properly designed and installed the protective device will prevent the cable from being damaged by overload.

So with your pattern of appliance usage it will either operate, in which case you'll know that a 16A circuit is inadequate, or it won't and everything will be OK.

 

[MalcofArabia]

yeah for them 2 items but if you have boiler, tvs and dvds on ect... aswel as the heater and kettle

We now move onto something called design When an electrcian designs an installation he will take into account all the possible appliances that can be plugged in.

Therefore he would install either a ring final circuit for the upstairs and another for the downstairs, and yet another for the kitchen

He may decide that rings are not right so perhpas he may install 2 20amp radial circuits upstairs 2 20amp radials downstairs and another 2 for the kitchen.

So now you have a 16amp radial where you seem to want to plug a whole lot of heavy duty devices in, so it may pay you to run another radial, see if it's possible to upgrade that 16amp to 20amp, not use the kettle and the boiler together.

 

[ericmark]

Does it matter? You select the MCB according to fixed wiring and equipment so with a 2.5mm cable reference Method 101# (above a plasterboard ceiling covered by thermal insulation exceeding 100 mm in thickness) one is permitted 17A and so one uses a 16A MCB this can feed a 100 sockets and you can plug in a 100 items which could use well over the 16A but as the current used crosses the curve of current time it will trip the 16A MCB before the cable overheats so there is no problem. It fails safe.
Only when supplying medical or safety equipment is there a problem. For example lights.

 

[ajrobb]

Sometimes the MCB has been de-rated to protect an appliance and/or flex. If you have the original design, it might show the radial is capable of 20A.

 

[mbga9pgf]

Sometimes the MCB has been de-rated to protect an appliance and/or flex. If you have the original design, it might show the radial is capable of 20A.

Can I ask, we have a 50A submain in our annexe. as I read the diversity regs, I cannot have little more than a 10kw shower and a cooker (10A+30%) on this circuit as it pretty much will be on the 50A MCB limit (16mm t+e submain , clipped in free air throught).

can I assume that as the shower will only be on for around 10 mins max, its unlikely the cooker will be drawing max load at the same time and any additional load (TV/lights etc) will only push me marginally above the 50A limit, that the circuit is legal?

Without going to fuses, I couldnt find any MCBs above 50A and I dont want to go to the hassle of a new supply installation.

 

[Adam_151]

Domestic consumer units are not designed to take circuits in excess of 50A

If you need more than you, its time to start splitting the tails and installing a separate switchfuse

I trust this installation is still in the design stage, and its already installed and you are trying to fit the design to what you have fitted...

 

[mbga9pgf]

Domestic consumer units are not designed to take circuits in excess of 50A

If you need more than you, its time to start splitting the tails and installing a separate switchfuse

I trust this installation is still in the design stage, and its already installed and you are trying to fit the design to what you have fitted...

The main CU has 100A rated incomers. Yeah, cooker circit isnt yet installed. Problem is, we only have an 80A (rural) rated supply for the main house plus annex. I dont think we can go much above 100A...

The "design" was an inherited feature of the house. They had 6mm t+E sullplying a cu with 10mm t+E to the shower

The submain is wired to the Main CU as I say in 16mm, with a 50A rated CB. The RCD at the end of the submain is rated to 63A. all I am asking is, if I install a cooker, are short duration 5-10% exceedences permitted across the MCB? I checked the graph, its well clear of the trip time at these current levels.