electrical Regs on connection before consumer unit....

[guydewdney]

I am trying to 'use' all (or as much as I need) my power before it gets exported.

To this end - I think I will use a reverse power relay - well - several.

this needs to be put into the wire in between the main meter and the consumer unit, with a small (500w or so) take off to a heater. Circuit breakers can be easily added into the system - but each one would need its own ELCB (is that what they are called still - the magic one at the end) - which seems OTT for each appliance.

What do the regs say? Im guessing everything has to go through an ELCB, before going round the house.


Basic circuit:-

outside world---reverse power relay(3)-----rev pow relay(2)-----rev pow relay(1)---normal cons unit
                         I                                    I                        I                      I
                       500w load                        500w                 500w                 water wheel

so that as the wheel generates more than we are using, RPR(1) sees 501w going right to left, and fires up heater. now theres just 1 watt being exported (ok - more like 50 watts). When the wheel is doing 1000+ watts, the RPR2 kicks in, and second heater gets a look in etc.

How do I stand? Is there sucka  thing as a single fuse / earth trip thingy I can use?

[noah]

guy
see my thread 
http://www.navitron.org.uk/forum/index.php/topic,8319.0.html

[daftlad]

There is no reason why you shouldn't block out the tails, fit another consumer unit (with an RCD (elcb)) and put 3 breakers and 3 contactors, which would feed the heaters, into the consumer unit.
I am not sure about your description of the reverse power relay, can you elaborate?
ta ta

[northern installer]

Guy,2 things you need between the meter,and your tails,before you start diverting things all over the place;double pole isolation (if single phase) or 4 pole isolation(if three phase) and circuit protection for the cable,sized for cable protection,and rated for maximum fault current.A 100 amp bs88 hrc switchfuse will probably do.

[guydewdney]

This is the problem - you cant feed contactors from one RCD  as the power from that RCD needs to come from the point just 'upstream' of where its measured.

to the right of the RPR there is (say) 2000 watts flowing.

the RPR sees this, and diverts off 500w to the heater. Now to the left of the RPR is 1500 watts.

The next RPR now sees 1500 watts, and diverts off 500 - etc etc

If the outgoing 'wasted' power is diverted before the sensor, then the sensor doesnt see the power, and will ossilate. (ie - 500 watts out - RPR switches - then sees 0 watts - so switches off... repeat). If the load is switched AFTER the RPR then even after it has fired, it still sees the same power flow, so stays on.

Any clearer - or as muddy as my leat?

[northern installer]

why do you want all these rcds?

[daftlad]

I have figured out what you are on about, I think?
I am not sure that it needs to be that complicated, that said it may need to be more complicated.
The problem you have is... if you measure the current on the tails the device sensing the current can not tell which way the current is flowing, so you may end up switching all of the heaters on when the wheel is stopped! 
So you need to measure the current being produced by the wheel, and the current been used by the house and then if the difference is plus 500 watts then you divert and so on.
What do you propose to use to sense the current flowing and then activate the relay?
If you have some Idea of the gear you want to use we certainly can come up with something.
The French have a device that does a similar thing but opposite, if the current in an installation goes above a certain level then non essential circuits (heaters etc) are switched off.
ta ta

[tony.]

guy,

can you post a link to the power relays you are going to use, it would be better to see the spec before deciding what is and isnt required

tony

[guydewdney]

http://www.pentagoninstruments.com/acatalog/Reverse_Power.html
this is on fleabay at the moment.

heres a better documented version
http://www.hobut.co.uk/protection_relays_reverse_power.htm
http://www.hobut.co.uk/relay/reverse%20power.png.pdf

Reverse power relays detect the current flow and direction. they are normally used to shut off a generator to the grid to stop it motoring when the prime mover goes down / underspeed.

example:-
3kw from wheel.
1kw to house
2kw to heaters required.

IF the heaters were supplied from the same RCD as the house, then as soon as the relay kicked in, the RPR would see 0 current flow, and thus switch back off, dropping the load. So the load needs to be 'after' the sensor (CT clamp). I'm not sure what the hysterisys is - but it sure as hell isnt going to be 100%!

so the 'load' needs to be after the sensor:-

wheel----house----sensor----load----outside

if it were
wheel---house---load----sensor---outside

it wouldnt work, as soon as the load kicks in, the export current (ie reverse) drops to zero (or at least down a lot) and the RPR (which is wired 'backwards' to detect current out of the system) drops the load.

Take it a stage further:

wheel---house---load1----load2---load3----sensor----outside

if at a moment in time the sensor sees 1kw out - and kicks in load 1 and 2 - then it sees zero again. So it has to be:-

wheel---house----sensor----load1----load2----load3----outside

In fact it has to be several sensors - as the RPR is just a single on / off device:-

wheel---house----sensor1---load1----sensor2----load2 (etc)


Does that make more sense?

Whats this french thing?

[Ted]

Guy, maybe I'm missing something but couldn't you simplify things by having the three heaters (I presume you need 3, rather than 1, as they are in different rooms) on a single dedicated circuit.


outside world-----rev pow relay------normal cons unit
                              I                      I
                       500w load            water wheel
                              I
                       500w load
                              I
                       500w load
       
The relay just needs to pass all it sees upto 1500W into that circuit and any more goes to export. The power would be equally shared amongst the heaters though.

[northern installer]

the output from your wheel generator will need to be very stable or the sensors are just going to jump in and out?

[crispy]

Guy,

I don't understand why you are talking about RCDs. Surely RCDs are a separate topic that protect the main household circuits running from your main consumer unit. You don't need any RCDs on your 'dump' loads or connected to the RPRs do you?

maybe I'm missing something but couldn't you simplify things by having the three heaters (I presume you need 3, rather than 1, as they are in different rooms) on a single dedicated circuit.


outside world-----rev pow relay------normal cons unit
                              I                      I
                       500w load            water wheel
                              I
                       500w load
                              I
                       500w load
      
The relay just needs to pass all it sees upto 1500W into that circuit and any more goes to export. The power would be equally shared amongst the heaters though.

Taking Ted's idea one step further, if you do this idea, then presumably if you don't want to evenly share the power then you could use a more simple current switch on the output from the RPR to control the various loads supplied by it. Since current will only be flowing in one direction (from the RPR to the 500w loads) the current sensing can be done using an unsophisticated sensor.

Edit: Ignore that, completely stupid, what a ridiculous idea. Of course, it won't work.  .

Ted's idea sounds good though, if you are OK to have current sharing between loads.

[northern installer]

there is so much baloney bandied about by those who only half understand electrical regulations:unless you are on a tt supply,rcds are only required on final circuits that are: feeding a bathroom or other 'special' area,supplying socket outlets,or if the circuit wiring is unprotected and concealed with less than 50mm cover.
RCD main switched consumer units didnt even comply with the 16 edition,'split' dual rcd only comply under certain circumstances,and as for '17 th edition consumer units' well if you fit one of those,there is no need for a book of regulations is there ? ?

[guydewdney]

OK - I think theres a slight misunderstanding. I dont want to switch on all three heaters at the same time - sometimes I will be exporting 510 watts - so I want to switch on one 500w heater at that moment. Other times there will be more. Hence three (or more) RPR's and 3 (or more) heaters.

The cable from the RPR in the 'mill room' where the incoming supply / consumer unit is, to where I want the heat, is quite a long way. What sort of protection do I have to have for that wire? As drawn above - there is NO fuse whatsoever - only the 100 amp jobbie the DNO put in. Obviously I need a little more protection than that.

[northern installer]

Guy,you need circuit protection to suit the cable size and length,but surely you dont intend to run the tails all that way?