Connection of back-upgenerator to TN-C-S domestic installation

if you look at the double pole diagram that Andy posted above, the NE link of the DNO is out of loop when on genset, so that's OK. 
Dont worry about the DNO earth being surcharged by any fault at your end that will be cleared within 0.2 secs - so you need some sort of RCD on the generator, perhaps 100mA time delay if you really care about discrimination with house RCDs, though I might not be so worried, a 30mA RCD on genset only trips with the double whammy of DNO fault and another one on your side knocking out one or both  RCDs - that is not likely and may be an acceptable risk - perhaps one preferable to a risk not tripping if there really is a fault at home.
Mike

im use to referring to island mode = floating neutral at generator

Ah, OK. I was using island mode in the sense of your installation being separated from the grid (power wise).

This is my concern if I'm using generator the DNO supply will be off line likely due to a fault and if I've all earths tied to DNO earth and ive a fault at my end will this not sent fault current through the DNO Earth/neutral onto to network?

An earth fault in your installation will (presuming the generator don't just stall or its output voltage collapse) may well create voltage differences around your own earth loop - but your earth loop will be referenced to Earth at some point - if your connection to the DNO PE is at the same point, you probably won't be exporting any voltage differences to them.

   - Andy.

Hi gkenyon, thankyou for the discussion grateful to you.

gkenyon said:

The Type 1 would be required in the garage ... but also because of the MET in the house, one might be required on entry of the feed from the garage at the house

I had miss-typed that question............" effectively type ! installed" should of said "type1 installed locally" (in garage db given garage is TT). Im proposing type 2 in the house new db because under normal operation supply from DNO is TN-C-S..

Im not fully understanding "on entry feed from garage at the house" for clarity the garage isn't at any time supplying or feeding the house, the garage gets its supply from the house db at all times mains/proposed generator supply.

My proposed supply from the generator will be from (outside and behind) the garage run out from generator outlet socket the temp supply cable will be run on the ground along side but outside of the garage building and into the 32amp single phase inlet mounted on the outside of the house the other end of this inlet is what will be going in electric cupboard and what i propose a 20amp rcbo then on from this to the manual bypass (make before break).  Is it the "generator supply" your referring to buddy? you think would do no harm a type 1 SPD in the rcbo housing prior to manual bypass ? .

gkenyon said:

Prosumer' is defined as combining a consumer installation with generation ... yes, original intention of including Chapter 82 was to facilitate renewables, but the definitions are what they are, and the 'modes of operation' are identical ... In fact, a local generator is shown (2nd item from top-right) in Fig 82.1. Any combination of items in Fig 82.1 and it's effectively a PEI. Have a look at Regulation 823.

Yes your correct in what you've stated under term "prosumer" within regs (thankyou for highlighting), generally applies to myself producing owner power during power failure "grid terms" "island mode" . When id looked over regs 823 as you have also stated this what id taken from it.

Regulation 826.1.1.2.1 discusses the earthing arrangement required for operating in island mode. A  suitable earth electrode should be installed within the PEI. There is no requirement to disconnect any earthing that is originally derived from the public distribution network e.g. TN-S or TN-C-S (see Figure 4.1).

For what im proposing the generator (neutral and earth linked) and 10mm earth cable from the earth pits id installed for garage, grounding the generator this would keep everything outside at equipotential.

When review further regs continuing 826 to 843 within Figure 4.1 as ref in 826.1.1.2.1 

It is important to note that operation modes are temporary and capable of changing. Earthing should be appropriate to whichever operation mode is active at that moment in time and shall be capable of reversing back to its previous state when the operating mode changes again, for example from direct feed to island mode and back again. 

Any change of type of system earthing for island mode shall be reversible as operation in this mode can be temporary, and the PEI can then be operated again in connected mode.

Regulation 826.1.1.2.2 determines that all live conductors shall be disconnected from the DNO supply including the neutral conductor when the PEI operates in island mode.  Following the 'break before make' philosophy, the neutral and earth of the PEI shall be connected. This is done to prevent incorrect operation of residual current devices (RCDs), but is not done until after the double-pole island mode isolator has opened.

Regulation 826.1.1.2.3 describes the connection to the local earthing arrangement using a transfer switching device to facilitate the connection to the earthing arrangement of the local star/mid-point or the local exposed conductive parts.

What i interpret from this , earthing arrangement is to be appropriate for mode of use and changed back when operating mode changes, to me this warrants switch earth to suit the new power source.

Fig. 4.1 Earthing: An electricity supply company may provide an earth at the point of connection but its primary function is protection of the network upstream from the installation. Under the requirements of the Electricity Supply Quality and Continuity Regulations (ESQCR), the consumer is responsible for ensuring that the installation is satisfactorily earthed.

 Regulations 26(1) and 26(2) of the ESQCR require the consumer’s installation to be:"...so constructed, installed, protected and used or arranged for use so as to prevent, so far as is reasonably practicable, danger or interference with the distributor’s network or with supplies to  others." 

My thoughts here when operating in PEI and in grid terms "island mode" ,"consumer to responsible own earthing" , "earthing arrangement using a transfer switching device to facilitate the connection to the earthing arrangement of the local star/mid-point or the local exposed conductive parts" and by using a switched earth to customers own earthing system (in emergency use /island mode) whilst isolated from DNO. regulation is fulfilled "reasonably practicable, danger or interference with the distributor’s network or with supplies to  others." as i am only generating during mains failure tbh 99% time is this is due to a network fault, earth switching would prevent fault current back feed from DNO and indeed if i have a fault when in "grid terms" "island mode" no chance of me introducing earth fault onto DNO grid.

4.1.1 Operating modes and earthing: Regulation 826.1.1.1 reiterates that PEI will change operating mode and that “protection of persons and properties shall be provided in all operating modes”. Where automatic disconnection of supply is used the system earthing used may differ and vary according to the operating mode in use at that point in time. 

a) For direct feed and reverse feed modes the PEI is connected to the public distribution network and 786 earthing of the PEI is the same as the public distribution network.

b) In island mode, when the PEI is disconnected from the public distribution network, the system earthing arrangements of the PEI may differ from the public distribution network whilst island mode is operational. 

4.1.2 Changes to earthing arrangements . For simple electrical installations, earthing arrangements are static and are only amended if the actual installation is altered. BS 7671 generally prohibits any form of switching in the circuit protective conductors of the installation to ensure that there is a continuous path to earth under normal and 794 emergency operating conditions.

The different operating modes of a PEI provide particular challenges and to mitigate this a special safety case needs to be implemented. BS 7671 Regulation 537.1.5 permits a switching device in the earthing arrangements where there is more than one source of supply providing certain conditions are met:  "...a switching device may be inserted in the connection between the neutral point and the means of earthing, provided that the device is: (i) a multipole, linked switching device arranged to disconnect and connect the earthing conductor for the appropriate source at substantially the same time as the related live conductors, or  (ii) a switching device interlocked with a multipole, linked switching device inserted in the related live conductors such that the earthing conductor for the appropriate source shall not be interrupted before the related live conductors and shall be re-established not later than when the live conductors are reconnected.

" 806 807 808 Earthing arrangements need to be assessed carefully at the design stage and each mode considered in turn  with mechanisms to change earthing arrangements if the mode of operation changes. These mechanisms need to be reversible, as stated in Regulation 826.1.1.2.1 :  “Any change of type of system earthing for island mode shall be reversible as operation in this mode can be temporary, and the PEI can then be operated again in connected mode.”

gkenyon said:

sland mode' does not mean 'floating neutral'. Please see Definition in Part 2 of BS 7671, and usage in Chapter 82. (Regulation 824.2)

your quite right , thankyou for the correction, was thinking "island mode" just generator powering 1 appliance not in terms of grid and a network 

Hi Mike thankyou. could you possibly explain out of loop, all earths appear to connect at MET in andys drawing

you think any earth fault would stay / dissipate with in my earthing system?, the earth rod link to the house MET would be via supply cable in event of power outage with gen in operation and linked to MET then just dp bypass, then run 10mm cable from genset frame to earth pit ive the garage earthing connected from.

Thanks again appreciate the discussion/advice

Kendo51 said:

Is it the "generator supply" your referring to buddy? you think would do no harm a type 1 SPD in the rcbo housing prior to manual bypass ? .

Yes, but also back out to the garage ... if the garage or generator gets hit by lightning, the lightning can back-feed to the house through either the generator cable, or the sub-main to the garage.

please forgive me for back-tracking slightly, but there's a subtle yet important point about the supply regs (ESQCR and equivalent). the OP is absolutely right, micro-generation isn't classed as a "generator" under the regs. However, many of the requirements about generation apply not to "generators" but to "any person" with a genset. this is how you "may be caught" by those requirements 

Hi gkenyon, and thankyou again for taking the time directing and highlighting issues to me i do appreciate it.

gkenyon said:

Yes, but also back out to the garage ... if the garage or generator gets hit by lightning, the lightning can back-feed to the house through either the generator cable, or the sub-main to the garage.

Just so i understanding /clarity. as per my framing on the original questions

Kendo51 said:

I supplied the garage with a 6mm armoured  via 30ma RCD and 40amp MCB ,armour being connected to house distribution board and isolated at the garage termination so as not to export the earth as per regulation,I installed 2m deep electrode and additional 1m deep electrode both wired back to garage DB. So in effect garage is on a TT system.

So currently the garage supply cable(sub main) from house db to the garage db, (to elaborate on above statement) is underground with armour(earth) connected in house db (for cable circuit protection only) the armour(earth ) is isolated from any metallic surfaces at the garage end.

I have 2 earth pits outside the garage one approx 4m from garage db (this has 2m of earthing electrodes and 2no.10mm earth cables back to esco prior to garage db connection)the other earth pit is approx 7m from garage db and has 1m earthing electrode and 2no. 10mm cables back to esco joining first earth pit cables in the esco, then from esco ive 2no. 10mm  earth cables terminated into the garage db, then finally 1no. 10mm earth from esco bolted onto steel garage framing .

Kendo51 said:

5. The generator chassis will be connected to garage earth electrodes when in use.

so elaborating from above, as the generator location is out back of garage and within (1.5m of the garage building) i was proposing running earth cable from nearest earth pit with (one with1m earthing electrode 4m away) to the chassis of the generator keeping all extraneous parts equipotential. House is some 7m from garage with no extraneous metal parts in between these points

1. If I install as above would any lightning not dissipate via the above earthing arrangement? would this not only potentially happen if i did indeed terminate all earthing arrangements at the MET as one?

2. My thoughts of the( switched earth) within manual bypass mains/gen selector switch was to prevent this very thing, stopping any fault current during a "mains failure" generator supplying the house event being referenced back to "DNO supply/earthing as more than likely DNO would be under fault condition during mains failure

3. If you think on it currently the metal garage has an isolated earth from the house db/DNO supply and garage earthing arrangement is via earthing electrodes (TT) so "as is" any fault current / lightening would be this path as there is no earth referencing back to house.

4. What is your thoughts on switching earths (during mains failure) for what I'm suggesting having reviewed all regulations/guidance including ones you'd kindly also highlighted ? do you not find that having reviewed it acceptable? from what i can ascertain from them is an allowance to do so in specific circumstances of which I think i would fall under .

Appreciate your thoughts

Ken.

Hi Dave, Your quite alright and thankyou for contributing to the discussion.

gkenyon has be really good throughout this discussion highlighting and pointing me in the direction of different regs etc below is a part of that discussion relating to what you have kindly contributed. If you could if you've time to review below inno it regs and long and tedious but think the thread/content is helpful . Hopefully you can see my reasoning within it. Any and all thoughts and feedback are welcome, maybe bias but I'm of the thinking what I'm suggesting doing is permitted after regs review and again further review to regs  gkenyou directed me to. Feel free to disagree / query /question any and all it helps the discussion from multiple view points.

Kendo51 said:

Section E part 1:(page 7) Citation, commencement and interpretation.  (**parts of note**)

" distributor"

Since the Regulations do not differentiate between licensed and non-licensed operators, the requirements apply equally to owners and operators of both public and private electricity networks **supplying** industrial, commercial and residential consumers or street furniture (see definition of network). The term distributor is intended to encompass operators transmitting and distributing electricity under the terms of the Electricity Act 1989 (as amended by the Utilities Act 2000).

"generator" (page 8)

For the purposes of the Regulations, generators operate high voltage equipment and are particularly associated with the provision of electrical energy to consumers via networks (see definition of network). The intention here is to include medium and large scale generating plant incorporating substations and electric lines to which the public may have access.

**Operators of any sort of generation in domestic situations are not expected to comply with the requirements placed on generators.**

However, all operators and consumers should note that they **may still be caught** by the requirements of Part VI Generation. Generators should note that they are exempt from implementing certain requirements within generating stations (see regulations 12 and 16).

So within the ESQCR guidance notes "generator" **may be caught by** part VI Generation, lets take a look at this:

J. GENERATION (page 31) (PART VI) 21. Switched alternative sources of energy.

21 This regulation deals with islanded mode only, i.e. a source of energy which operates as a switched alternative to the supply from the local distributor’s network.

An example of such an arrangement would be an emergency standby generator which is called upon to **generate after loss of the supply from the distributor’s network**, and which is disconnected before the load is transferred back to the supply from the distributor’s network following restoration.

When supplying load, the switched alternative source of energy is never connected **in parallel**with the **distributor’s network**, even for short durations.

In these circumstances operators should ensure that the switched alternative source of energy cannot be paralleled with the distributor’s network.

In particular, operators should comply with the principles enshrined in BS7671 Requirements for Electrical Installations (see definition at regulation 1(5)) and the Electricity Association’s Engineering Recommendation G.59/1 (Amendment 1, 1995) Recommendations for the Connection of Embedded Generating Plant to the Regional Electricity Companies’ Distribution Systems. It should be noted that these Regulations do not deal with sources of energy supplying installations which are not connected to distributors’ networks. Such installations should comply with BS7671.

**With all the above reviewed I see ESQCR regulation/,conditions satisfied with what I'm suggesting,  apologies if I'm misconstruing, I'm open for correction.

With ref to:

gkenyon said:

A 3-pole transfer switch is unlikely to meet the requirements of G99 (or G99/NI) and hence legal requirements (ESQCR).

G99/NI again is mainly regarding paralleling, syncing and exporting to the network/grid. **lets get a look** 

Find out more about the Distribution Code for Northern Ireland | Northern Ireland Electricity Networks

Page 11: 2.5 This document applies to systems where the Power Generating Module(s) can be paralleled with a Distribution Network. Where the Power Generating Module(s) can only be used as an alternative source of energy to supply the same electrical load within the Customer’s Installation the requirements of Section 7.4 of this EREC G99 apply.

So page 53: 7.4 Switched Alternative-Only Operation

7.4.1.1  Under this mode of operation it is not permissible to operate a Power Generating Module **in parallel** with the Distribution Network. Regulation 22 of the ESQCR (NI) states that it is the Generator’s responsibility to ensure that all parts of the Power Generating Module have been disconnected from the Distribution Network and remain disconnected while the Power Generating Module is operational. The provisions of this EREC do not generally apply and the **earthing, protection, instrumentation etc**. for this mode of operation are the responsibility of the Generator, however, where such a Power Generating Module is to be installed, the DNO shall be given the opportunity to inspect the equipment and witness commissioning of any changeover equipment and interlocking 

7.4.1.2 The changeover devices shall be of a ‘fail-safe’ design so that one circuit controller cannot be closed if the other circuit controller in the changeover sequence is closed, even if the auxiliary supply to any electro-mechanical devices has failed. Changeover methods involving transfer of removable fuses or those having no integral means of preventing parallel connection with the Distribution Network are not acceptable. The equipment shall not be installed in a manner which interferes with the DNO’s cut-out, fusegear or circuit breaker installation, at the supply terminals or with any metering equipment.

7.4.1.3 The direct operation of circuit-breakers or contactors shall not result in the defeat of the interlocking system. For example, if a circuit-breaker can be closed mechanically, regardless of the state of any electrical interlocking, then it shall have mechanical interlocking in addition to electrical interlocking. Where an automatic mains fail type of Power Generating Module is installed, a conspicuous warning notice should be displayed and securely fixed at the Connection Point

**And crucially** 7.4.1.4 The Power Generating Facility shall use an earth electrode independent from the Distribution Network.

**So with ref to the G99/NI and from my understanding of it, I'm complying by not syncing, exporting paralleling to the DNO/Grid and network, my generator is to be used in "mains fail state"  I will be using a manual "break before make" supply bypass switch.

With ref to the earthing arrangement my thoughts for switching earth within the manual bypass is exactly because of 7.4.1.4 and to comply with BS7671 maintaining cpc continuity and earthing protection/main and supplementary bonding for the installation

My additional thought is if DNO has a power outage with fault on N conductor my house supply being TN-C-S  id have no earth if had my generator earth connection tied to DNO and I'm running the generator to supply the house and it developed a fault the resulting fault currant would be back feeding onto DNO network . 

thanks

yes, there are some excellent points about G99 and ESQCR that have been made by more informed commentators than me

my minor point doesn't affect any of that, it just creates the link from your installation through the supply regs to the wiring regs. specifically, reg 22 of the supply regs covers "Where a person operates a source of energy" and reg 23 covers "a person who installs or operates a source of energy". you'll see that regs 22 and 23 don't apply to "generators", they apply to "person[s]"