Men System ?

[TS79]

Thought I'd throw in another electrical thread. Can the electrical gurus offer some advice to some questions.

I live in a moo baan approx 5 years old.

Pic 1 - There are high level wires (i assume MV?) feeding a transformer about 50 metres from my house.

Pic 2 - This transformer feeds a lower level set of wires (3 phase?) along the moo baan, the top wire is bare. I think the fifth wire from the top is the one which supplies the street lights from its own meter at one end of the street.

Pic 3 - Close up of pic 2, you can see 4 connections to these lower level wires. Top wire and second top goes to my meter, top and third top goes to neighbours meter.

Pic 4 - Approx every 3rd pole in the moo baan has a bare wire connected from the top lower level wire than goes down the pole into the ground.

Pic 5 - Electric Tester

Pic 6 - Consumer Unit

Is this system MEN?

If it is MEN, my CU doesn't have a MEN link installed (no connection between the neutral terminal bar and earth terminal bar), does a link need fitting?

The 'Electricians' who wired the houses in the soi when asked had no idea about what MEN was (maybe lost in translation). They did tell me that there was a earth rod fitted into the ground below the CU but I cannot confirm as the wires are hidden.

When I plug in my electric tester to the supply it indicates that wiring is OK, voltage is OK and that the loop test (resistance to earth?) is between 10 and 100 ohms which I assume is too high as the indicator LED is red, I guess it could be close to 10 ohms though which wouldn't be too bad but could also be close to 100 ohms which would not be so good. Should I install another earth rod and connect to the earth terminal bar in the CU to try and reduce the resistance? All sockets in the house produce the same results from the tester.

Currently all the breakers in my CU are MCB's (pic 5), the CU is Bticino. For safety reasons I would like to install the ThaiVisa recommended RCBOs but after trawling the bticino websites I cannot seem to find any from this manufacturer. Is it possible that other manufacturers RCBO will fit a bticino CU or will this be not possible? I guess I could install another CU and use the existing one for circuits that don't require RCD's and a new one for circuits that should be on RCBO's? Square D seems highly recommended and then I could move the circuits over.

Sorry for the long message but tried to get all my questions into it.

Thanks in advance,

T.

Edited October 15, 2012 by TS79

[David48]

You have a 'Panic Room' ...

If it really is a security room, you have the electricity feed on the same feed as the rest of the house?

[TS79]

You have a 'Panic Room' ...

If it really is a security room, you have the electricity feed on the same feed as the rest of the house?

Haha, nah its just my workshop / junk room but its entrance is through a bedroom and as it was being built it just took the name Panic Room (after the movie). You've got good eyes !!

[electau]

If you do not have a bond between the main neutral and the main earth your installation is TT, and RCD/RCBO protection is required on all circuits. 10mA and 30mA are available for retrofitting, modules are 18mm wide.

Your main earth connection should be accessible for inspection and testing. It would appear that the MEN connection is not used in your area. The distribution neutral is earthed at intervals to maintain the N to E potential to 0 volts.

The earth loop resistance of your installation is too high for a conventional MCB to operate within 0.4secs in the event of an earth fault, and this is why RCBOs are used on TT installations.

Are your MCBs plug in or DIN rail mounting ? Schneider, AAB, Clipsal, Merlin Gerin, Hager etc all manufacture single pole width RCBOs. to IEC standards.

[Crossy]

Can you post a photo of the consumer unit with the lid off? The normal Thai way of connecting MEN isn't immediately obvious and follows the NEC method of feeding the incoming neutral via the ground bar before it enters the main switch.

I believe the bticino CU takes the same plug in breakers as the Square-D units.

[electau]

The NEC method used in Thailand to implement the MEN is to connect the main earth conductor directly to the main neutral bar. The earth conductors may be connected directly to the neutral bar at the main switchboard (or a separate bar connected by a link or bond to the main neutral bar).

The AS/NZ method to implement the MEN is to connect the main earth to the main earth bar and all earthing conductors connect to the earth bar. There is a single link or bond between the main neutral and the earth bar. This is removed for testing purposes only.

The earth loop resistance with an MEN system should be less than 2 ohms, in practice it will be much less and this and will be depend on the current rating of the MCB and the type, B, C or D. C is the standard curve for most MCBs.

The incoming neutral of a MEN system must NEVER be switched, the neutral may be switched after the MEN connection, ie the load side, provided the Line and Neutral conductors are switched simultaneously.

[TS79]

Thanks for your replies so far.

Firstly I apologise as I thought it was possible to identify MEN from the power distribution outside (from the earthed N conductors). I am sure, however, that all circuit earths are connected to the earth terminal rail and all neutrals to neutral rail without any link between them. Is the difference between TT & MEN only whether or not a link is installed or is there a difference in the PEA infrastructure?

Attached are the requested pics of the CU, little bit messy I know.

On the neutral bar you can see see one small grey wire in hole 11, this wire joins to a red wire (with orange screw cap) but it isn't the red wire that is in the earth bar, it goes up to the roof space. I guess the sparkies must have ran out of white wire.

Pic 11 shows a label inside the CU that says it complies with IEC60439, so hopefully this might allow another brand of RBCO's to be fitted?

Thanks again for your time.

[Crossy]

OK, you are correct, it looks like your board is NOT wired for MEN.

A few observations:-

You really need to organise some form of earth leakage protection, either with an RCBO to replace the main switch, a separate Safe-T-Cut box or individual RCBOs on circuits for water heaters, wet room outlets and outdoor outlets (this would be an absolute minimum).

There is a worryingly small number of wires on your earth bar, I would run your Martindale over all your outlets to ensure they are actually connected to the earth.

Since your system is TT an earth resistance of 10 Ohms is pretty good, I expect that in addition to the rod your structural steel is connected to the earth bar making a decent ground.

[TS79]

Ok, so with this infrastructure it is not possible to put a MEN link in? What is the difference in infrastructure supplied by PEA that makes the system TT or MEN?

I am with you on the sparse number of earth wires but every outlet has been checked with the Martindale and all are earthed. When testing them the outlets I did find a couple of sockets that needed the Live / Neutral wire swapping over but apart from this all was good and a worthwhile exercise. I imagine that the earthing must be done in the roof space and only a couple of wires back to the CU. I've been in the roof a couple of times but its not as easy as being in the loft of a UK home where there are plenty of trusses to grab hold of so I try to keep visits in there to a minimum over here.

I would like to put individual RCBO's on the circuits that need them rather than one on the incomer. Which brand / device would you recommend? Do you have any link to a catalog page?

Thanks guys.

[electau]

Installation of RCBOs.

1. Install one RCBO , this is the lowest cost option but may be more liable to nuisance tripping. The existing MCBs are retained. You retain the existing main switch.

2. Retain the existing main switch and install 2 x 30mA RCBO units and split the circuits over the two. Medium cost option.

3. Install individual 10mA and/or 30mA RCBOs in lieu of the MCBs on all final subcircuits. Highest cost but the best protection. Retain the existing main switch.

Check the earthing of all 3 pin socket outlets and any other permanently connected electrical equipment.

With methods 1 and 2 You can install the RCBOs in a separate enclosure above the existing loadcentre.

As the load centre complies with IEC standards, alternative brands of protective devices may be fitted. mounting should be HAT section DIN rail. You should check first.

The existing main switch should be an 2 pole MCB. installed on the load side of the neutral bar.

　

Edited October 16, 2012 by electau

[Crossy]

Ok, so with this infrastructure it is not possible to put a MEN link in? What is the difference in infrastructure supplied by PEA that makes the system TT or MEN?

From your description the neutral does seem to be earthed at multiple points so it could be that MEN is implemented but just not in your home. Have you checked others (friends)?

It is extremely unwise to add a link unless you KNOW that you have a compliant installation, if you don't know leave it as TT.

Look here http://en.wikipedia....Earthing_system for a description of the various grounding systems.

I would like to put individual RCBO's on the circuits that need them rather than one on the incomer. Which brand / device would you recommend? Do you have any link to a catalog page?

The Bticino boards take plug-in MCBs and RCBOs. Obviously ones from Bticino would be the correct units but if you can't find them Square-D will probably fit (and are available in Homepro). Pop out one of the breakers and take it to your local electrical stockist to match fittings.

There does also seem to be a distinct shortage of neutrals so you are going to have great fun trying to find what neutral is tied up with each breaker, borrowing neutrals seems to be de-rigour for Thai sparkies and makes installing RCBOs a nightmare.

It may be easier to just go with a whole house unit (external or main switch replacement)

[TS79]

Ideally, even though the house is only 5 years old and 4 years lived in, I would like to rewire the house to a higher compliant standard as I don't like the single core twisted and taped connections at every light / socket and instead go in favour of the triple core insulated cable (similar to the UK twin and earth but all three conductors are insulated individually and overall). In the roof there are wires lying on top of the ceiling boards and would like to put some kind of traywork up running the length of either side of the house to carry the cables on. I'm from an industrial controls background and tray / conduit installations are what I'm most familiar with.

I think it may be wise to have the wife check with the PEA to see if they can tell us whether this moobaan had MEN implemented or not. We are not out in the sticks (Phuket) and the area is relatively new.

Another question, the meter I'm on is a 15/45. The feeder cables to the CU are 16mm2, with these feeders is it possible to upgrade the supply and meter to 30/100 or do the cables need changing out for 35mm2 (cable run is approx 15m)? Reason I ask is I have 4 AC's now, an electric oven and an electric water heater, although not all running at the same time.

[Crossy]

Another question, the meter I'm on is a 15/45. The feeder cables to the CU are 16mm2, with these feeders is it possible to upgrade the supply and meter to 30/100 or do the cables need changing out for 35mm2 (cable run is approx 15m)? Reason I ask is I have 4 AC's now, an electric oven and an electric water heater, although not all running at the same time.

15/45 is the standard house supply, PEA want you on 16mm² so that's OK. The next supply up is 30/100 and according to the PEA documentation I have (and our local office) that needs a 35mm² cable

The 15/45 will not blink at 90A for short periods so unless you start to see the main (63A) breaker opening I would not bother upgrading just yet.

[electau]

　

If you intend to install a MEN link you should check with the PEA for their requirements. The TT system is compliant as long as RCBOs are installed, and with the lack of testing of electrical installations in Thailand it would be the preferred option as the risk of a broken neutral conductor or the reversal of polarity of the incoming mains will not constitute a prospective hazardous situation in the short term. The incoming neutral at the switchboard should be clearly indentified (by testing) as well as the neutrals at the meter.

When installing RCDs you should check that you do not have any interconnected circuits or crossed neutral wires.

16sqmm with a 63A MCB will be quite satisfactory for your existing max demand requirements.

Use approved junction boxes for the connection of cables. J boxes may have loose or fixed terminals. There should be no single insulation of cables exposed outside of fittings.

[electau]

I have yet to see a compliant MEN installation in Thailand, they have all been a version of a TT system with individual electrodes or no earthing at all. All have been Thai owned.