Load Center: High-Rise Residential Building in Brazil

[Wilsonrio]

I would like to know what might be the best way to add ground to a load center located in Rio de Janeiro, Brazil.

Note: If the forum allows me I can post a picture of the load center I am describing.

Facts:
- Apartment is located on the 20th floor
- No easy access to rewire the entire apartment (metal conduit size, concrete walls, etc.)
- Service size 425 AMPs
- 120/240
- Three-wire system (2 hot, 1 neutral, no ground)
- No ground bus bar
- No neutral bus bar
- Loadcenter brand: unknown (GE?)
- Circuit breakers: 1 inch wide
- Most circuit breaker branchs have light and receptacles together

Questions:
Note: When the electrician connected a receptacle tester, the reading shows "correct", however I am not sure if the wiring was done correctly, background below:

1- Local electrician says that "neutral" wire works the same way as a ground wire, since there are only 2 wires (1 hot and 1 neutral) coming from the branch circuit breaker into the receptacle, the neutral wire will return to the load center and the neutral wire from the loadcenter will be connected at some point to the building ground. The electrician replaced "2-prong outlets" with "3-prong outlet without GFCI" connecting together in the receptacle "neutral with ground" using a small wire. Could this cause any safe hazard or interference (ground loop)? Is this correct?

2- Also in another receptacle the electrician replaced "2-prong outlets" with "3-prong outlet without GFCI" connecting the ground wire direct into the metal conduit. I am not sure if he is creating unnecessary multiple independent ground locations, that can cause interference or other problems in the future.

3- There is a need for only two receptacles to have ground done correctly. I would like to know if a "ground bus bar" can be added to the loadcenter panel, rewiring only one single branch circuit breaker (15 AMPs breaker -----> 15 AMPs receptacle) using 14/2. Will this work? Should the ground bus bar be connected direct into the utility neutral line?

4- The second receptacle has no access and it can't be rewired without major construction work. Can a "self-grounding" receptacle be used or there are better choices?

I appreciate your comments and suggestions.

Thank you,
Wilson

 

[bphgravity]

Re: Load Center: High-Rise Residential Building in Brazil

It sounds to me that they may have been using the metallic raceay as the equipment grounding means. If this is the case, you shouldn't have any issues properly grounding as long as you can ensure the continutiy and integrity of the metallic connections.

Most of the procedures you ask about indeed are unsafe and against code. I would investigate the situation further to determine if indeed the metal raceways can be used as EGC's, and then make all connections to receptacles and in the panel accordingly.

 

[hurk27]

Re: Load Center: High-Rise Residential Building in Brazil

By Wilsonrio:
The electrician replaced "2-prong outlets" with "3-prong outlet without GFCI" connecting together in the receptacle "neutral with ground" using a small wire.

If the receptacle grounding is in fact connected to the neutral in the receptacle outlet box then it is dangerous.
You never want to use a current carrying conductor for grounding, There are several reasons not to do this but the main one is voltage drop in the grounded conductor will be on all the grounding connected to the receptacle
If a ground fault was to happen while a person was touching a grounded appliance and another grounding path back to the panel there is a very good chance they could be electrocuted.
Another reason is if the neutral of this circuit become disconnected for what ever reason the return path would become the grounding. We call this boot legging the grounds and it can be very dangerous, What would happen if the polarity was reversed up stream from this receptacle?
A three light tester would still show the wiring good but now both the neutral and grounding is connected to the hot conductor and would have 120 volts to earth or other grounding paths. A good way to get someone killed!

Yes it needs to be fixed!

[ October 30, 2005, 09:08 PM: Message edited by: hurk27 ]

 

[thinfool]

Re: Load Center: High-Rise Residential Building in Brazil

Originally posted by Wilsonrio:
- No ground bus bar
- No neutral bus bar

If neither of these exist, how are connections made to allow a 120v branch circuit?

In my experience, most countries use 220v, 50hz or 60hz, for their 'point of use' appliances. I get the impression that Brazil has provided for 120 volt circuits as an 'after thought' by using the ground to also serve as a neutral.

 

[Wilsonrio]

Re: Load Center: High-Rise Residential Building in Brazil

Thank you for your comments.

The local electrician said that there is no easy way to add ground to an apartment (20th floor) that has 2 wire system (2 hot and 1 neutral). He is saying now that new 3 prong receptacles was grounded to the metal receptacle box and not the outlet. The receptacle's ground screw is wired with another wire to the receptacle's metal box, this metal box connects to a metal conduit that runs inside the concrete walls going back to the electrical service panel (apartment's load center). Sounds like that the loadcenter itself is acting as a grounding conduit. Was this an acceptable way to upgrade the outlets?

Is there any specific section in the NEC book, white papers or other electrical reference that addresses high-rise residential building (MDUs)?