to bond or not?

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mdechgan

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I have a question and need some advice.

1) There are two wires from the meter. One hot one neutral. Service does not supply a ground.
2) There is no isolater or service disconnect. The wires from the meter go directly into a square d main distribution panel and directly into a main circuit breaker which supplies other mini circuit breakers via the distribution panel.
3) The grounding rod is connected to the earth bus.
4) I am certain the transformer's neutral is grounded.


The question is should I bond the neutral to the ground or isolate them.
Currently the neutral wire goes into the earth/ground bus bar and then into the main circuit breaker so the neutral is grounded before the main disconnect. The ground from outlets are also conected to the earth/ground bus. So in essence the 3rd socket or ground socket is connected to neutral. Is this a parallel neutral circuit?

Should I isolate the earth and neutral or is ok as it is. I have consulted many and its 50-50. Some say it a boo boo and I should revert back to a TT system while some say its safest.

I don't know if this is a PME system or not? I don't have a main service disconnect other than this main panel.
 
To really understand how to install this task is to say you are actually a journeymen electrician. Sometimes an electrician can explain in laymen terms to non-tradesmen but this does not ensure understanding and understanding is what is needed to install this task.
 
mdechgan said:
Some say . . . I should revert back to a TT system while some say its safest. I don't know if this is a PME system or not?
Click to expand...
I don?t know those two terms (TT and PME). But I will echo Bryan?s question.

This Forum is for electricians, inspectors, engineers, and other persons who make their living from the electrical industry. I cannot tell from your member profile (i.e., ?management?) whether or not you fit into this category. But it appears to me that you are not an electrician. Your question makes me wonder whether you are planning to perform electrical work at your own home. We are not permitted to provide ?how-to? assistance to a ?do-it-yourself? person.

So I am going to ask that no member post any additional replies to this thread, until we are able to verify that the question relates to the OP?s profession.

Mdechgan: You can post a reply here, or you can send me (or Bryan) a private message.
 
I am located in Bangkok, Thailand.

This project is already installed, but I have to to approve and sign off on this work.

1. The sub contracted electrician did not impress me. I had to supervise and tell which wires were which and which colors he was supposed to use etc. So I do not trust this guy's work.

2. The electrical company only supplies the power to the meter. Anything after the meter is not the electrical company's liability.

3. The inspector was really rude and didn't really care. All he did was check if the wire gauges were correct and asked if their was a ground which I said yes. He didn't even bother to open the panel. All he said was the main circuit breaker was too large and I had to change it to a smaller amp. Which was really weird because the wire gauges were oversized and I wanted enough for future expansion.

4. There is no main service disconnect on the premises other than this square D breaker box. So in the main circuit breaker, distribution panel, service disconnect is one and the same.

5. I am not a certified electrician, but I am very knowledgeable in engineering especially industrial engineering where I have years of education and a degree. My purpose is to surpervise, be responsible, and approve various projects and service for many projects. So one can consider me a a project manager or building supervisor. So I have to sign off on the electrician's work and have authority to correct his work.

6. Voltages here are 220volts RST with a neutral. So amps are half of what you guys are used to. This current project we are talking about is residential. I calculate no more than a 30 amp normal load. Breaker is 60 amps. Wires are 35 sqmm or 2 gauge. Voltage drop is well within 3% limits.

The arguement here is there are two systems of grounding. A TT system is where the neutral and earth is isolated throughout the system The ground rod is connected only to the earth bus bar that all. Neutral is grounded only at the transformer. The other system or PME, MEN, multiple earth or TN-C-S is where the earth ground is connected or bonded at the source. Usually before at the service disconnect which there is none on this project. If this were a main board I would ground the neutral no questions. But this project still baffles me because after many consultants some say don't bond some say bond.

no:
The people that say not to bond because on a multiple earth system one can't guarantee other people's are earth. And its not a good idea to have the only earth rod on the entire system. He means other's faults will go through our earth system.

yes:
These guys say bond it because this is considered a main service disconnect and has to because of safety. There is no other way of disconnecting the power other than this main breaker. Grounding the neutral will help stabilize voltage and allow another path just incase the circuit doesn't trip incase of a neutral fault.

I would appreciate your guys help if you can help me clear this matter.
 
I don't think the voltage, or anything else matters other than at the point of service the neutral is bonded and nowhere else, other than additional alternate sources.
 
You shouldn't have taken on the job. If wiring in the states make you cringe, go overseas and you'll have real nightmares.

Matt
 
I did some searching and found out that there's a rule here where the neutral has to be supplied by the ground bus bar.
 
How about this: Take a look at this post, which is based on the NEC's requirements for a grounded American system.

I think the problem is, we are uncertain whether the NEC governs this installation. We're also unsure of what you are picturing when you use the term "ground", as it can mean a lot of different things.

Basically, what it boils down to is this: If the source (utility transformer) neutral is connected to the earth, then if there is a fault from a phase to the normally non-current-carrying metal enclosing the electrical components of the system (a phase to ground fault), then there is a shock potential on those parts. Current will travel along the phase conductors, to the point of fault, through the metal enclosing parts, through a person, through the earth and return to the transformer. There are many ways to deal with this problem.

The most conventional NEC-compliant way to deal with the issue is to create a dedicated Equipment Grounding System at the service disconnect. The utility neutral is bonded to this system, to create an intentional bonding path back to the source, to cause the service disconnect (or branch circuit circuit breakers) to open in the event of a fault.

The only role the earth plays in this scenario is creating a need to make a better path than the earth to open circuit breakers.

Other means to deal with the issue that are outside the NEC's preferred method is to install an RCD (essentially Ground Fault Protection of Equipment) at the service disconnect, to sense that there is a problem and shut power off in that event. This is common practice in areas other than the U.S.A.

I am only familiar with work done under the NEC in the USA, as are many here, so that makes me (and probably others) uneasy offering advice for systems outside that comfort zone.
 
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