BS5467

[Catford Bags]

Hi All - just starting to plan a DIY 4KW (ish) groundmount system. This may not be the only question that I post on here...

 

My current plan is put the panels 60m from the house beside an existing shed. The shed is supplied with electricty via a buried underground cable. The cable comes out of the consumer unit in the house, is trenched under the garden then has a t junction - one half supplies the sockets and lighting in the shed via a small consumer unit, the other half used to supply a static caravan but is now capped off in an exterior box.

 

The AC armoured cable is BS5467 (600/1000v). 3 core 10 mm. CSA.

 

i'm not a spark. My question is - Could my design incorporate the existing cable to transport electicity from the consumer unit in the shed (which would contain my proposed inverter and battery) back to the house ?  IE - can I avoid having to trench another cable.

Many thanks in advance for any thoughts.

Edited January 31 by Catford Bags

[TonyT]

[TonyT]

I lost my post, so if it was my house, I wouldn’t stress, I would have suitable labels, isolators in place, double pole RCD protection, not shown in the regs snapshot above but that’s perfect world, engineering decisions have to be made.
 

etc but it’s your spark doing the install that needs to sign it off.

 

How are you going to measure the current on the taiks via a CT?

 

 

[ProDave]

Voltage drop is going to be your issue.

 

Voltage drop for 10mm is  4.7mV / Amp / Metre

 

So at 16A and 60 metres that's 4.5V drop.  That is per core, so total volt drop = 9V

 

That mainifests itself as voltage rise when the inverter is generating.

 

Most inverters will shut down or power limit at 253 volts.  So with that much volt rise, if your house voltage exceeds 244V your inverter is likely to either shut down or reduce power.

 

I would first measure your typical mains voltage and see how close you are .

 

With long runs it is better to do a large part of the run in DC cables with the inverter close to the house.  Volt drop on the dc side does not usually cause any issues.

[Dillsue]

Some things to consider- 

As ProDave mention volt rise could be an issue but you can mitigate it. Some inverters allow you to reduce power generation as the voltage rises. If you are happy to do this then pick the correct inverter. As loads are switched on in the house the house voltage will likely drop a bit so when measuring your base voltage do it with 1, 2, 3 and 4kw loads switched on to see how the base voltage varies at different load levels and the likelyhood of the inverter power throttling. If your no load voltage is less than 244vac, then likely you've not got a problem with voltage rise.

 

If you've got a battery to charge that's local to the inverter then voltage rise may not be an issue if you are routing power to the battery and not down the SWA. As TonyT mentions, to charge your battery when there's no load demand from the house you'll likely need a CT on the supply leaving the house and need to consider how the CT signal will get from the incoming supply to your inverter/battery. You might be trenching 

 

If your battery is AC coupled then how are you going to limit the current that flows down the cable from the inverter and battery. If your battery is DC coupled are you sticking within the 16amp G98 limit.

 

 Ground mount PV has planning restrictions and I think you are limited to 9m2 without getting permission. You may not be concerned, but worth knowing the limitation.

 

If you might extend the array in the future then base your design on the extended array size/location

[Alan Ambrose]

There was a similar thread on here recently. From brief research, I came to the same conclusions as above - the majority of people run DC back to an inverter near the house CU, with the inverter not so very far away from the CU that a current clamp can't monitor the overall DNO supply.

 

Lastly, I think the power can't go from the outbuilding into the house CU via the RCD/MCB that it is currently hanging off. First, it'll make the house CU live even when the CU isolator switch is operated - which is 'not great'. Also, the house CU may very well have the wrong RCD - it needs a more grown-up one (forget which, type B maybe) for the inverter. (FFS there are 6 or 7 RCD types these days!)

 

A question for @ProDave - why do we generally put outbuilding CU's hanging off an MCB/RCD in the house CU rather than straight from the DNO supply (i.e. in a similar fashion and 'parallel' to the to the house CU)?

Edited January 31 by Alan Ambrose

[Dillsue]

2 hours ago, Alan Ambrose said:

the majority of people run DC back to an inverter near the house CU, with the inverter not so very far away from the CU that a current clamp can't monitor the overall DNO supply.

The OP is trying to avoid running another cable out to the outbuilding. If the existing is used for the PV DC therell be no AC supply to the outbuilding

 

2 hours ago, Alan Ambrose said:

I think the power can't go from the outbuilding into the house CU via the RCD/MCB that it is currently hanging off. First, it'll make the house CU live even when the CU isolator switch is operated - which is 'not great'. 

That's the way all grid tied inverters are connected as they shutdown when they loose their grid connection.

 

 

[Alan Ambrose]

>>> The OP is trying to avoid running another cable out to the outbuilding.

 

Yeah, I am saying I think that's unrealistic.

 

>>> That's the way all grid tied inverters are connected as they shutdown when they loose their grid connection.

 

That strikes me as iffy. I much prefer the layout for non-grid tied e.g.

 

I think that set-up needs a bit of work too - presumably you would want the 'critical loads' on their own little CU. I guess the outbuilding supply could come off the house CU or (better in my view) before it. And I don't see an RCD on there for the inverter. I see some RCDs and RCBOs are bi-directional. Also, in most cases, there's clearly some work to do re earth protection.

 

 

Edited February 1 by Alan Ambrose

[JohnMo]

Here is a thread I started prior to doing my ground array.  Approx 4kW split into two. No way it would 60m without a voltage drip too big or huge cable. Ended up doing 4x6mm2 armoured cable to inverter, approx 60m away.

 

 

 

 

[Dillsue]

22 minutes ago, Alan Ambrose said:

>>> The OP is trying to avoid running another cable out to the outbuilding.

 

Yeah, I am saying I think that's unrealistic.

 

>>> That's the way all grid tied inverters are connected as they shutdown when they loose their grid connection.

 

That strikes me as iffy. I much prefer the layout for non-grid tied e.g.

 

I think that set-up needs a bit of work too - presumably you would want the 'critical loads' on their own little CU. I guess the outbuilding supply could come off the house CU or (better in my view) before it. And I don't see an RCD on there for the inverter. I see some RCDs and RCBOs are bi-directional. Also, in most cases, there's clearly some work to do re earth protection.

 

 

That's a grid tied set up with back up. The grid tie is the AC connection coming out of the bottom of the inverter then running to the left out towards the grid without any means of automatically disconnecting from the grid. If the grid goes off so does the inverters output to the grid and the consumer unit, so the consumer unit is dead. The inverter you are showing has a back up output for critical loads but needs a grid connection to operate fully ie power the loads off the main consumer unit.

 

If the outbuilding supply came off before the CU, then its protected by the DNOs service fuse so a fault in the outbuilding would take out the service fuse(or fry the cable) and black out the house, likely for a long time until the DNO got out to replace the fuse. If you add your own fuse/mcb to protect the outbuilding cable then you might aswell have the outbuilding supply coming off the CU and not before it.

[HughF]

The ‘grid’ port on the Sunsynk is bi-directional apparently. Separate output for critical loads, and separate generator input.

 

It’s no outback, but it seems to do the job.

[ProDave]

On 31/01/2024 at 16:32, Alan Ambrose said:

A question for @ProDave - why do we generally put outbuilding CU's hanging off an MCB/RCD in the house CU rather than straight from the DNO supply (i.e. in a similar fashion and 'parallel' to the to the house CU)?

Choose the cable method between CU and outbuilding to not require an RCD you can connect it from a non RCD protected MCB in the CU.  It will require a high integrity CU.

[Dillsue]

12 hours ago, HughF said:

The ‘grid’ port on the Sunsynk is bi-directional apparently. 

I guess it would need to be so it could power the critical loads/charge the battery from from the grid when there's no PV??

[Bramco]

27 minutes ago, Dillsue said:

I guess it would need to be so it could power the critical loads/charge the battery from from the grid when there's no PV??

 

On the Sunsynk, critical loads are a separate connection - there are 3 ac connections on the Sunsynk Ecco inverters: grid which is bidirectional, critical loads and one for a generator/wind turbine.

 

We've just fitted one of the 5kW inverters with 3 of the 5.1kWh batteries and are very happy with it - so far.....    The instructions for setting up how the power flows are a bit crap though, took a few tries before we go all the right boxes ticked.  

 

We have a 6.5kWp solar ground mounted array (with planning permission, we're green belt, so had to apply). Our sparky also advised a DC cable for the array to the garage which is about 60m distance. So as per @JohnMo's post above 4 core armoured cable.

 

Simon

[HughF]

On 03/02/2024 at 09:42, Bramco said:

 

On the Sunsynk, critical loads are a separate connection - there are 3 ac connections on the Sunsynk Ecco inverters: grid which is bidirectional, critical loads and one for a generator/wind turbine.

 

We've just fitted one of the 5kW inverters with 3 of the 5.1kWh batteries and are very happy with it - so far.....    The instructions for setting up how the power flows are a bit crap though, took a few tries before we go all the right boxes ticked.  

 

We have a 6.5kWp solar ground mounted array (with planning permission, we're green belt, so had to apply). Our sparky also advised a DC cable for the array to the garage which is about 60m distance. So as per @JohnMo's post above 4 core armoured cable.

 

Simon

Sunsynk ask for over current protection on the gen and load ports, then omit to fit them onto the AC board. They managed to fit one onto the grid portion of the board 🤦‍♂️

[Catford Bags]

Thanks Everyone for your really helpfull responses. I am a total layperson where it comes to electricity but it does seem from your responses that at 60m, the sensible solution is to trench a DC cable and location the inverter/battery inside the house beside the CU.

 

Thanks again for helping with that decision. Will now post another thread re high level design thoughts.

[TonyT]

Sensible solution would be to add a duct and run cables in duct to allow extra cables such as CT cabling or data to be added..

[sharpener]

One thing no-one has mentioned is that an ESS inverter should be protected by an RCD which it does not share with any other circuits. Several of the systems upthread do not comply with this.

[Alan Ambrose]

I thought we covered that, no? Also, should really be a bi directional class B RCD as inverters often have dodgy output waveforms.

[Catford Bags]

On 31/01/2024 at 09:11, ProDave said:

Voltage drop is going to be your issue.

 

Voltage drop for 10mm is  4.7mV / Amp / Metre

 

So at 16A and 60 metres that's 4.5V drop.  That is per core, so total volt drop = 9V

 

That mainifests itself as voltage rise when the inverter is generating.

 

Most inverters will shut down or power limit at 253 volts.  So with that much volt rise, if your house voltage exceeds 244V your inverter is likely to either shut down or reduce power.

 

I would first measure your typical mains voltage and see how close you are .

 

With long runs it is better to do a large part of the run in DC cables with the inverter close to the house.  Volt drop on the dc side does not usually cause any issues.

Just quick update - i've been doing further research re the voltage drop issue. I would still like to use the existing cable if possible (there is an existing cat 5 cable trenched alongside it - can this be used for the CT signal ?)

 

I measured the base house voltage - and it moved between 240-242V

 

With a 3.68 inverter - the voltage drop calculation suggests 1.37% rise. (ProDave - do i need to double that because of the number of cores in the cable ?)
With a 5kw invert - the voltage drop calculation suggests 2.5% rise.

 

I'm considering either the GivEnergy Gen 3 Hybrid 3.68kw or 5kw inverter but I can't see on the datasheet at what point power limiting/shut down happens..... The data sheet shows The Output data (AC) Nominal Voltage / Range 180VAC - 270VAC - https://midsummerwholesale.co.uk/pdfs/giv-hy-5-0-gen-3.pdf

[Alan Ambrose]

>>> there is an existing cat 5 cable trenched alongside it - can this be used for the CT signal ?

 

I think you would be going into somewhat uncharted territory. The problem is sending a smallish analogue current - say, between 5 and 50mA over a long-ish distance (long-ish for analogue electronics purposes anyway) without getting significant signal mangling or noise interference. Yeah, maybe - you might want to try it out if you have time, a simple burden resistor and an oscilloscope. Maybe someone else already has. Pretty much anything with electronics is possible in terms of converting X to Y, or converting this signal to that signal. But it'll probably be too much effort. It also won't be 'following the manufacturer's installation instructions' and so might be difficult to get BC sign-off if you need it.

 

I did see an inverter recently that used a proper power meter which mounted on a din rail (can't remember which brand but I was looking at inverters that do islanding). The power meter produced RS485 protocol which is a proper digital industrial control signal - robust and good for electrically noisy environments etc.

 

You could then feed the RS485 on one or two of the unused pairs in the CAT5 (you can get some splitters which allow you to do this without making custom terminations) or a RS485<->ethernet adaptor at both ends.

 

I wonder though, with that kind of complication, whether you would just setting yourself up for later trouble as you would be the only one who understood the set-up. A typical spark probably wouldn't get it as it's 'digital electronics' rather than 'power electrical'.

 

I do see that good sparks are getting some experience with RS485/ethernet etc now and, of course, industrial sparks do - so I don't want to do anyone here a disservice.

 

Edited February 29 by Alan Ambrose

[Dillsue]

Having an RS485 connected energy meter monitoring the import/export is the std way that Solaredge do charging/export limitation. I don't know if Givenergy have that option or rely on a CT directly connected to the inverter. If they rely on a direct CT connection then either the CT signal would likely travel a reasonable distance or they'll be limiting the use of their inverters by needing them to be mounted near to the incoming supply. You should be able to get that info from Givenergy??

[Alan Ambrose]

I see GivEnergy do have a modbus current clamp, so you just need to ask them which of their inverters it'll run with:

 

https://www.tradesparky.com/solarsparky/accessories/meters/givenergy-em115-meter-with-ct

 

 

[Dillsue]

11 hours ago, Catford Bags said:

 https://midsummerwholesale.co.uk/pdfs/giv-hy-5-0-gen-3.pdf

Data sheet says that's got an RS485 interface to an energy meter and the battery, so you'd be able to use your cat 5 cable to run RS 485 between an energy meter on the incoming supply and an inverter in the shed.

 

With a base voltage of 240vac ish you're not likely to have volt rise issues at your inverter based on your calcs