Craftsman To Check Grounding Of Electricity Of House

[naammanow]

Great info Mr Angry. I have installed in my house a W-OP4 Digital Phase Protector. It is situated before the main switches. I have 3-phase, coming from the 50KV transformer via this protector to the main fuses. If and when it cuts the electicuty to the house it always informs me that it is the "Unbalanced" voltage that is the culprit. And lately seems to cut quite a few times a day. Any idea why this might happen and do I really need this unit. I rather fit a Safe T-cut unit instead, however will it be big enough to carry the loads?

[naammanow]

re my last post, herewith a picture of the unit installed.

[naammanow]

Sorry, think my attachment did not materialise; herewith again.

[dhrobertson]

Great info Mr Angry. I have installed in my house a W-OP4 Digital Phase Protector. It is situated before the main switches. I have 3-phase, coming from the 50KV transformer via this protector to the main fuses. If and when it cuts the electicuty to the house it always informs me that it is the "Unbalanced" voltage that is the culprit. And lately seems to cut quite a few times a day. Any idea why this might happen and do I really need this unit. I rather fit a Safe T-cut unit instead, however will it be big enough to carry the loads?

A phase protector is to protect 3-phase equipment from damage if a phase is lost or if the voltages on each phase differ by more than, say, 10%. It does not protect against shock. For shock protection, you could fit a single, large ELCB/RCBO/RCD. These are available for 3-phase systems. However, as yours is a larger installation, I would have your electrician install individual ELCBs/RCBOs on circuits which require protection. (All circuits supplying water heaters or socket outlets). In this way, if there is a fault, you only lose power to that one circuit. These ELCBs replace existing circuit breakers. ELCB should be same current rating as the breaker (MCB) replaced and have a trip rating of 30mA.

I suggest you adjust the phase protector to be less sensitive. +/- 15% would be fine. If a single phase is lost or has very low voltage, you can get an effect called double phasing at 3-phase rotating machines. This can cause motors or compressors to be damaged.

Edited March 27, 2012 by dhrobertson

[Dellboy218]

Great info Mr Angry. I have installed in my house a W-OP4 Digital Phase Protector. It is situated before the main switches. I have 3-phase, coming from the 50KV transformer via this protector to the main fuses. If and when it cuts the electicuty to the house it always informs me that it is the "Unbalanced" voltage that is the culprit. And lately seems to cut quite a few times a day. Any idea why this might happen and do I really need this unit. I rather fit a Safe T-cut unit instead, however will it be big enough to carry the loads?

A phase protector is to protect 3-phase equipment from damage if a phase is lost or if the voltages on each phase differ by more than, say, 10%. It does not protect against shock. For shock protection, you could fit a single, large ELCB/RCBO/RCD. These are available for 3-phase systems. However, as yours is a larger installation, I would have your electrician install individual ELCBs/RCBOs on circuits which require protection. (All circuits supplying water heaters or socket outlets). In this way, if there is a fault, you only lose power to that one circuit. These ELCBs replace existing circuit breakers. ELCB should be same current rating as the breaker (MCB) replaced and have a trip rating of 30mA.

I suggest you adjust the phase protector to be less sensitive. +/- 15% would be fine. If a single phase is lost or has very low voltage, you can get an effect called double phasing at 3-phase rotating machines. This can cause motors or compressors to be damaged.

In my industry known as single phasing, at which point the rotating machine will make an almighty noise, most likely stop and start drawing a stall current at which point one hopes the overload trip works before the motor burns out. Safe T Cut themselves make 3 phase units up to 125 Amp. I agree, if it is something simple caused by a heavy load cutting producing a momentary drop on one phase then adjust the unit, I believe you can also adjust the time on that unit as well to allow for transients. Hopefully it will not be the supply or bad connections.

Edited March 27, 2012 by Dellboy218

[dickyknee]

Please be sure of the facts when giving advice.

There are two reasons for having a ground connection

1) By connecting exposed conductive parts of all equipment to the main body of the earth, there can be no potential difference between anything and therefore no chance of shock.

2) A separate ground allows faults to be identified and circuits to be disconnecting automatically.

Whereas neutral is connected to ground at the transformer star point and several other points, it actually supplies current during 50% of the cycle. In a single phase ac system, the phase voltage alternates beteen +220V RMS and -220V RMS 50 times per second. This is why neutral and phase ("hot") are both considered to be "live". Both wires carry current and therefore exhibit potential (voltage).

A separate ground has been required on most circuits in thailand for many years (including for luminaires less than 2.4m above floor level).

Usually, best ground performance is achieved using TN-C-S ground system. This involves bonding neutral to ground at the main load panel and adding ground rods to achieve less than 5 ohms to the main body of the earth. (Use 3m, copper clad steel rods, typically 3 in a delta array). Yes connections by exothermic welding are good (and common in Thailand), but compression joints are generally fine.

ELCB/RCD/RCBO protection is required for water heaters and certain other situations in Thailand. International standards require this protection for socket outlets. For small installations, I recommend a single main ELCB (Safe-T-Cut or similar) SET TO 30mA.

Problem in Thailand is that "electricians" are not licenced and generally have no knowledge of the THai EIT code.

Also, new installations are supposed to be checked by the PEA/MEA before a meter is installed. Sadly this almost never happens.

I will answer specific queries if contacted directly.

sorry to nit-pick, RMS by definition can't be anything but an absolute value. the actual voltage it swings between are ~ +311V and -311V (for a 220V phase voltage) reference to Neutral.

otherwise, i've got nothing to add to your informative post...

[dhrobertson]

Yes, thanks for pointing that out!

RMS is going to be absolute value. In fact peak voltage is of course root2 x 220V nominal.

For those in the dark, when we talk about 220V a.c., this is this equivalent d.c. voltage that would provide the same heating capacity as an a.c. voltage of +/- 311V. (622V peak to peak).

It's a comfort that someone knows what they're on about, to coin a Yorkshire expression!