Can RCD/GFCI replace earthing/grounding? 3

[Power0020]

In LV application, for personal safety if a 30 mA RCD/GFCI is fitted to the terminal load, would it matter if the equipment body/chassis is earthed/grounded or not for RCD operation if someone touch the faulty housing? (as long as it is not connected to the neutral).

It may be a code mandate to connect every metallic structure to earth/ground PE conductor as this makes sense for MCB operation with ground fault current in case of insulation failure to have a quick fault clearance and protecting against shocks.....I don't know if this still mandatory to operate the RCD? the RCD will trip once someone touches the faulty equipment chassis(unless the chassis is buried in concrete walls then it will leak through back to supply and trip it, otherwise it will only trip once touched).

Any clue? code refereces?

 

[che12345]

Dear Mr. Power0020 (Electrical)(OP)
Please tell us a little more:
1. Are you in the IEC or ANSI/NEC world, so that we can refer to the relevant Standard/Code. Note: IEC requirement differs from that of ANSI/NEC.
2. If in the IEC world, which [earthing system] (e.g. TT, TN-S, TN-C, IT .....) are you refereeing to ?
3. We may be able to post some opinion after knowing the system.
Che Kuan Yau (Singapore)

 

[Power0020]

Dear Mr.Che,
Thanks for your reply,
1-I am in IEC world, but would like to know the NEC world opinion in that.
2-This is probably a TN-C system in most places of 3rd world countries where just two wires are available at homes.
3-Thanks again!

 

[stevenal]

A GFCI operates based on imbalance between the two conductors. NEC recognizes this and allows them to retrofit old two prong installations as long as they are marked as ungrounded.

 

[dpc]

The GFCI would function properly, but the installation would likely not be in compliance with the NEC unless the equipment is properly grounded and an equipment grounding conductor provided, assuming this is a new installation. Article 250 in NEC covers grounding requirements.

 

[Kiribanda]

If a 30mA RCD or GFCI is installed it will operate for a current unbalance of 30mA. That means even the hot wire is touched to the wall
slightly it will trip. But in NA & most of the NORDIC countries the walls are mainly made of wood and other somewhat non conducting insulted
material due to weather conditions thereby creating even 100mA leakage current to the wall is very difficult. In contrast, the walls of the
buildings in ASIAN and other countries are mainly made of using cement, sand etc. so that there is considerable amount of MOISTURE inside the wall
which will help to create even 10mA leakage current possible.

NA NEC wiring system is mainly a TNS system so that earth leakage protection is provided by overcurrent devices (MCCBs). In this system
EGC is a must so that leakage current is taken back to the source via EGC, bonding jumper & the neutral conductor. But now NEC
specifies RCD/ GFCI for certain critical branch circuits so that even the EGC is missing or not connected properly, the RCD/ GFCI
will trip for a 10mA or 30mA leakage thereby human safety is ensured. In other words, earth leakage protection is provided
by RCD/ GFCI devices which is better and reliable than providing same earth leakage protection by overcurrent devices like MCCBs/ Mcbs.

The answer to your question is even though the branch circuit is RCD/GFCI protected, not providing an EGC to each metallic enclosure
is still a code violation.

It should be also noted here that if the equipment is "DOUBLE INSULATED" with double square symbol (ex. electric iron), does not
need an EGC. This double insulation is an European concept now getting popular in NA due to global business similar to EX "e"
concept in hazardous area applications.

 

[che12345]

Dear Mr. Power0020 (Electrical)(OP)7 Sep 22 08:40
"...#1. I am in IEC world, but would like to know the NEC world opinion in that. #2. This is probably a TN-C system in most places of 3rd world countries where just two wires are available at homes."
#1. NEC requirements had been covered by others.
#2. FYI: In IEC, [TN-C] system implies that only the power source Neutral is earthed. Distribution: (Neutral and Earth) are combined into [one conductor PEN]. For a single-phase load [Phase L (brown), Neutral (light blue), Earth (green/yellow); where the Neutral and Earth are connected to the PEN.
#2.1. the Phase shall be (over-current protected) for faults between [Line and Neutral or over-load]. This Line-to-Neutral fault current will not be picked up by the RCD.
#2.2. Equipment conductive housing shall be Earthed. Consider when the conductive housing is NOT earthed, and a high resistance fault between the Line and the housing, charging it up to the Line voltage. Neither the MCB nor the RCD would trip. However, any person touches the housing and with current exceeding 30mA will trip the 30mA RCD.
Che Kuan Yau (Singapore)

 

[Power0020]

Thanks everyone. useful thoughts.
Are RCDs mandatory with double insulated appliances? I have seen many of these appliances comes without an earthing connection even.

 

[Kiribanda]

Per IET 18th edition/ BS7671 RCDs are not mandatory with double insulated equipment because it has two layers of insulation.
When the first insulation is failed the second one is still there. The same socket outlet that used to plug a double
insulated equipment not having an EGC may be used to plug a non-double insulated equipment having EGC at the next moment.
Therefore, finally RCD/GFCIs ae used for all branch circuits.