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WDMDL

Is there a readily available current detection device that can be used to disconnect one circuit as the other exceeds a set current? With or without integrated contactor?

This is for use in a large static caravan which has many high-load appliances such as 2.5kW washer, 2kW tumble dryer, 2kW oven and 2.2kW of electric heating.

I want the space heating to be disconnected automatically for the short periods of time that the loading on the socket circuit exceeds 25 Amps, so there is no possibility of the 32A shore supply breaker tripping.

Simon.
 
a current sensing relay and contactor would do that-if you can get one in 25amp

or even an overload and separate contactor


basic discrimination on your mcb's is prob simpler

or get a suitable supply
 
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Hi Simon

This is the sort of thing I live for! In fact, I have a similar application for something very similar, I've done a bit of searching.
I can't find anything "off the shelf" plug and play, but I didn't really expect to.
I found these but I havent investigated deeply enough to determine which one would be most suited
Single Range AC Current Operated Switches
They seem to have outputs that switch on if the current passing through the sensing hole rises above a variable set point.
These outputs could easily switch a contactor to control your heating.
First thoughts would be to place the sensor in the cable feeding everything except the heating. The set point would be determined to only allow the heating on when there was sufficient power available to supply it. The down side to this is that it couldn't make allowances (without resetting the set point each time) for any heating that was installed but not drawing current, either because it was switched off becuse it was in an unused guest bedroom, say, or because the room stat was satisfied and not calling for heat at that particular time. An other issue may be that a rapid cycling themostat may cause the heating to be constantly switched on and off. A stat on a cooker ring perhaps. This could be rather inefficient.
A further issue may be that these devices may be slightly slower to react than the circuit MCB. This would not be a problem for switching on the heating but may be risky
if something else was switched on resulting in an overcurrent for a few miliseconds whilst the the sensor and contactor operated. The tripping time of the expected overcurrent would need to be assessed. My gut reaction would be that it is probably OK, but it would be worth checking out first.
I would be interested to hear of anything else you may find.
 
Thanks all, especially Bluetobits who has hit the nail on the head with that link.
The ACS150 (Normally Closed version) should fit the bill perfectly and be able to control a small 20A contactor directly.

I had considered thermal overloads but rejected them on the basis of response time.

The space heating is at present connected via switched fused spurs into the nearest available socket outlet, but as part of this work these will be recovered and a separate 16A radial will be provided.
This new circuit, in conjunction with the contactor, will allow simple switching of all heating simultaneously (no running about checking each and every one!) and also enable the heating to be remotely controlled (GSM interface) in the future.

Response time of the ACS150 is 120ms`so with the response time of the contactor being something similar or better, any potential overload should only be present for a maximum 0.25 sec so should never be an issue.
I don't envisage any problem with cycling the space heating (convectors) in response to (eg) the oven stat, as they have their own internal bimetal thermostats and seem to cycle about every minute anyway as the setpoint is maintained.

Thanks again,

Simon.
 
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