AMPS LIMIT

[Meister]

I understand the mathematics of working out how many Amps a given piece of electrical equipment uses but what about this:

If a hook up is rated at 16Amps is it a) safe and b) possible to use 16Amps without tripping the circuit breakers ??

The same applies of course for any other rated hook up.

Steve

 

[Alistair_5094954]

a) Yes

b)Yes,if the circuit breaker is rated for 16Amps and above.

The 16 amp rating doesn't mean that there is 16 amps coming out of the hookup.It means you can connect equipment that takes up to 16 amps of current.In which case you must have a 16A rated circuit breaker in the caravan.

Although hookups (the socket) may have a rating of 16 amps many have a 5 amp or 10 amp circuit breaker fitted before the socket,this means the hookup would be rated for 5 amp or 10 amp even though the socket is rated for 16Amps.

 

[JeremyClarksson]

Some items particularly ones with motors like vacuum cleaners draw a high initial current so even though they could in theory make up a total current pull of 16A you might find that the initial surge might trip the circuit.

 

[rayc]

Some items particularly ones with motors like vacuum cleaners draw a high initial current so even though they could in theory make up a total current pull of 16A you might find that the initial surge might trip the circuit.

The MCB should be chosen with that in mind i.e. a type B , C or D which allow higher initial inrush currents of defined values for specified time period.

 

[Meister]

Thanks for the info but you have now thrown up another point.

Given that some pieces of equipment i.e microwave oven, use an initial high surge of power how can I work out what that will be ?

E.G.: 750 Watt microwave uses 750 Watts which equates to 3.26 Amps BUT if there is an initial surge WHAT Amps are needed ??

Steve

 

[JeremyClarksson]

I guess only the manufacturer of each piece of equipment could give those details, but if you were to switch off the heaters while you started such equipment I would imagine it should be OK.

What equipment are you thinking of running together for this level of current?

I think the MCB would have a built in surge tolerance.

 

[vernon]

A 750 watt microwave takes a lot more than 3.26 amps.

750 watt is the output and they are not 100% efficient.

 

[Rod_5041370]

The data plate on my 750 watt microwave states that the input current is 1080 watts.

 

[Meister]

SO in relation to Rods 750 watt oven:

750 watts divided by 230 volts = 3.26 Amps

1080 watts divided by 230 volts = 4.69 Amps

which means that when/if we buy a microwave for our 'van we need to check the INPUT wattage to get an accurate measure of power requirement.

Or .......... have I got it wrong ??

Steve

 

[Rod_5041370]

That's correct Steve, it's always the current drawn from the mains that is important and not the output wattage.

 

[Meister]

Thanks for clearing that up .... it makes sense now.

 

[Rod_5041370]

Steve,

Out of interest, I have just checked the microwave that is built ito my caravan (the one above is the one in the house).

The output wattage is 500 watts and the power consumption is 950 watts.

 

[Meister]

Thanks Rod. We were thinking of something along the lines of a 500 watt as it will only be for use in the 'van.

Steve

 

[oldievanner]

Even though our microwave in van is 950 watt power consumption it is still fitted with a 13amp fuse in the plug.

 

[Rod_5041370]

Peter,

If the power consumption is 950 watts at 230 VAC, then your fuse rating may be a little high as it will only draw around 4.2 amps.

 

[ProfJohnL]

Hello

The topic has turned towards microwave ovens, and it has correctly been stated that it is the input power from the mains that needs to be considered.

Microwave ovens are not the most efficient at converting input energy into useful heat, hence the higher input wattages compared to the output. The over factor with Microwave ovens is that most of them have a surge current when you turn them on. The exact amount is not always stated but it can cause an initial inrush current that is substantially more than the rated running current. To cope with this the appliance may need the 13A fuse in the plug.

Also most microwaves with have an internal fuse on the input supply line. These are usually rated to be closer to the normal running current, but are of a design known as slow blow or anti surge. These will accommodate the ovens excess current for a very short while, but will blow if the surge is too long. Many of these are not designed to be user replaceable.

As always read the manufactures instructions, and always replace a blown fuse with one of the correct rating.

 

[Rubix]

Meister said : "If a hook up is rated at 16Amps is it a) safe and b) possible to use 16Amps without tripping the circuit breakers ??"

This is more of a question, but somehting to think about. Regarding point b)

Yes, the plugs and sockets are rated at 16 A, but even if there is a 16 A circuit breaker in place, how many people can draw power that adds up to a possible 16A. In other words if there are 4 sockets on one power point will that mean that 16 A is available as long as the combined current of those four outlets does not exceeed 16 A ?

I have only been to a couple of sites with electrical hookup, but it was not made obvious what the outlet was rated at, so I was ultra careful and I have an current/power meter that I can keep an eye on to see if I will go over the limit (I used this at home to see what all my mains appliances draw).

 

[ProfJohnL]

Hello Rubix,

I have read your posting several times, and I hope I have understood what you are asking.

A circuit breaker will only respond and affect the systems connected down stream of it. So regardless of how many items are connected to it, it will be happy until the sum of the actual currents of the appliances exceed the threshold limit of the breaker.

If a 16A breaker is used to supply a number of 16A sockets, then all the sockets can draw current provided that the sum of the currents at any time is less than 16A. It also means that only one socket can supply the full 16A at any one time. IF the total current through on or more sockets exceeds the trips threshold then all the sockets will be disconnected.

It would be normal to assume that if a 16A Ceeform socket is available then it is capable of supplying 16A. If it is limited to a lower current then it would be courteous to inform users of a limited supply.

 

[Meister]

Re point b) of my initial question: - thanks for the replies. I do understand that the TOTAL amps available will be as shown on the hook up.

Now to the microwave matter lol.

Surely if a 750 watt microwave oven (or other appliance) has a power consumption stated as being 950 watts then any initial (or otherwise) surge can NOT exceed this ?

Is it not correct to expect the power consumption stated by the manufacturer to be the MAXIMUM wattage ?

Or am I missing something here lol ?

Steve

 

[gary]

I don't think the inrush current is stated, only the running current but either way the correct MCB caters for it.

MCB's are rated by amps followed by a letter a,b,c,d, these denote it's overload capacity and for what time. 'a' is instant c&d are mostly for industrial use and a very heavy overload for a short time.

'b' is the common a garden domestic type your most likely to see, these are designed to take 1.45 their stated load for a considerable time without tripping, go above this even fractionally and the time reduces dramatically.

Actual overload values vary from new within tolerances and are therefore stated as 'more than' less than', constant tripping further changes these values throughout it's life.

The bottom line then is you get what your given on site and have to work with it, but if one MCB is troublesome it's always worth swapping to another if that's possible.

 

[Meister]

So if I understand you Gary, it is possible that a microwave could draw up to 10amps which is the fuse on my vans MCB covering the 230 volt sockets ?

Ridiculous situation really when trying to work out what appliances I can run at the same time !

 

[ProfJohnL]

Hello Meister,

I can understand you confusion on this. However I don't think you need to be unduly concerned. An inrush current lasts for a small fraction of a second, and in its self is unlikely to be enough (unless it is truly excessive) to cause a problem to the MCB or the correct fuse.

In these days of micro electronics we tend to think that electrical devices act instantly, but in the case of MCB's and RCD's they are designed to have a small delay in operation to account for such things as inrush currents.

In well designed products the IRC should be suppressed so it doesn't cause nuisance tripping of fuses, MCB's and RCD's

The types of product that may have an IRC are those that have a significant inductive load such as motors, or products with large transformers (esp. the toroidal type as found in large audio power amplifiers) and to some extent fluorescent lights, compressor driven fridges, and microwaves.

For the purpose of estimating your current consumption, the values derived from the appliance data plates should be satisfactory.

 

[gary]

To give you an example based on your vans 10A MCB and assuming it's a 'b' grade which will be shown alongside '10A'.

A 10A b will give 1.45 it's rating which is 14.5A for perhaps 15 or more minutes without tripping, however if the load was 16A then the time will reduce to perhaps 4 or 5 minutes.

To put this into reality, our vans MCB is a 10amp 'b', we get caught out if the fires on 2kw while the water heater is on, (630w), and we switch the 2kw kettle on, this is a total of 20amps!! but it still takes roughly 30 seconds to trip. However still with the water heater but the fire on 1kw, then the kettle has chance to boil and switch off before the MCB trips and that's 16amps from a 10amp breaker for a usable length of time.

So as I said it's not an exact science, even the manufactures don't know exactly how any particular breaker will perform? so you will only ever be able to estimate and experience will tell the truth.

I might add though, these usable overloads I'm speaking of are designed in to stop the nuisance tripping you fear.

 

[Meister]

Thanks guys.

I am sure you understand that as a newbie to caravanning I dont want to turn up on sites and start tripping their circuits on the hook up ...... unhappy wardens/owners !!

I just feel happier knowing what appliances I can have on at any given time, particularly as we intend to use the van over the winter months too.

Steve

 

[MalcolmL]

I have found recently that if I happen to switch on too many appliances, it is the MCB in the 'van which trips rather than the one at the bollard.