Multiple Circuit Ground Lines Question

[topher]

SquareD consumer panel, RCBO Main breaker...

Let's say I have 6 breakers and circuits running out to outlets, lights etc in my house.

I'll be using conduit in walls and a PVC channel from the panel along the top of the main wall.

So I was planning on running black/white pairs and single conductor green wires for each circuit.

Do I really need to run 6 seperate green wires out thru the channel and split off them according to circuit path? It should be electrcially the same to run a main green wire down the channel and run greens off that to each outlet, light etc. It seems pretty wasteful to run so many greens when they all tie into the exact same earth bar...

While I kind know I could do this and save a lot of wire but is there a good reason not to, or code that would expressly indicate every circuit must have it's own green?

Thx again.

Edited March 17, 2012 by topher

[prefabs]

if your "main" green wire gets damaged, what is your backup plan?

[attrayant]

Not sure what the code is here but in the US it's common to daisy-chain ground wires from one box to the next, or simply to clamp on to the nearest cold water pipe if it's certain that the plumbing is all copper. I've never heard of a ground wire being damaged unless some clueless worker blindly cuts into it. But that would cause the same problem whether you daisy-chain or not.

Edit: after reading again, I see you're not really talking about a true daisy chain. You want to run a main ground and then have "drops" every so often when you need to ground a service outlet. I think as long as you use a good, tight mechanical bond such as wire nuts or a screw terminal, it should be electrically sound. Please don't pigtail the drop around the main ground run and leave it at that.

Edited March 17, 2012 by attrayant

[Crossy]

It's not something that would be done in the UK, but I see no electrical reason not to. Just ensure the main ground conductor you use is big enough for the largest circuit expected to use it.

For safety I would keep things like water heaters on their own ground back to the earth bar.

EDIT You may consider using Scotchlok insulation displacement splices to attach your droppers, no need for cutting and stripping. NOTE 3M do make mains rated (600V) Scotchlok connectors, but the ones commonly available are intended for low voltage automotive use so they are not suitable for your live (L & N) wiring, should be good on the grounds though. Got to be better than Twist-n-tape.

[T_Dog]

It's not something that would be done in the UK, but I see no electrical reason not to. Just ensure the main ground conductor you use is big enough for the largest circuit expected to use it.

For safety I would keep things like water heaters on their own ground back to the earth bar.

EDIT You may consider using Scotchlok insulation displacement splices to attach your droppers, no need for cutting and stripping. NOTE 3M do make mains rated (600V) Scotchlok connectors, but the ones commonly available are intended for low voltage automotive use so they are not suitable for your live (L & N) wiring, should be good on the grounds though. Got to be better than Twist-n-tape.

Good points as always Crossy. I have seen oven heating elements short to the grounded oven floor back in the USA so that makes a good point for using a wire heavy enough for the possible currents.

[topher]

Thanks for the suggestions.

I may run 3 grounds then. 1 for hot water, 1 for light fixtures and 1 for outlets.

My plan was to use wire nuts for all wire-wire branches.

[electau]

Each final subcircuit should have its own individual protective earth conductor which

is connected to the earth bar.

It is possible to use one individual earth conductor to each point that requires earthing, eg lights. socket outlets, hws, airconditioners. Minimum size in this case is 2.5sqmm. This method may be found in older installations. Joints in wires are soldered.

If you are using conduit you will be using single insulated PVC wires, use 2.5sqmm earth minimum.

Edited March 18, 2012 by electau

[Crossy]

Each final subcircuit should have its own individual protective earth conductor which

is connected to the earth bar.

Whilst this is the Aus and UK regulation is there any electrical reason why an adequately sized ground conductor should not have droppers to each point requiring a ground? It would certainly save on cabling.

My only reservation would be the potential loss of all grounds in the event of a single joint failure. Use of a tap-in type of connector such as the 3M Scotchlok or pigtailing and soldering the droppers without breaking the main ground cable would remove this potential single point of failure.

We use a similar (but rather bigger) earth distribution system in metro stations, a large earth bar runs around the equipment rooms to which the individual equipment ground cables are bolted, this has a single (large) earth mat on the other end. Note, this is the electrical safety ground not a clean functional ground, that's another copper bar.

[electau]

Each final subcircuit should have its own individual protective earth conductor which

is connected to the earth bar.

Whilst this is the Aus and UK regulation is there any electrical reason why an adequately sized ground conductor should not have droppers to each point requiring a ground? It would certainly save on cabling.

My only reservation would be the potential loss of all grounds in the event of a single joint failure. Use of a tap-in type of connector such as the 3M Scotchlok or pigtailing and soldering the droppers without breaking the main ground cable would remove this potential single point of failure.

We use a similar (but rather bigger) earth distribution system in metro stations, a large earth bar runs around the equipment rooms to which the individual equipment ground cables are bolted, this has a single (large) earth mat on the other end. Note, this is the electrical safety ground not a clean functional ground, that's another copper bar.

No reason at all. The joints should be soldered or the connections should not be able to readily disconnected. Was used in older electrical installations under AS3000. Min conductor size 2.5sqmm.

[topher]

I was planning to use 2x1.5 (double insulated) even in the conduit since it's less costly than using two single (black and white). I don't think there's a reason not to have the extra insulation and it keeps circuits tidy since you can easily see each circuit in the trunk channel to the panel.

The Thai 3 conductor wire available here is all 2x1.5+1. The green earth is downgraded in size and according to Thai docs around they also suggest using smaller green. Is this just silly Thai cheapness as they still don't believe in running an Earth? Or is it really quite ok? I don't plan to use this 3 conductor wire and instead run separate Greens.

I'm not eager to run a main 2.5 sq.mm green line since I could run several 1sq.mm greens for lower cost. Unless you really recommend running Green same size as B+W. My largest Live wire is 1.5sq.mm since I've now decided to not use a hot water heater but add a solar heater instead.

The locals all think hot water is just silly, and to some extent that's true. But I would like to take the chill off winter showers and I think solar will do at least that.

Edited March 23, 2012 by topher

[Crossy]

The idea of reduced ground conductors is common, in the UK 2.5 twin and earth has a 1.5 ground conductor.

The old idea of having the earth the same size as the main conductors was belt and braces from the days before RCDs. Cost cutting is of course the main reason for the smaller conductor. Part of the system design process is to ensure that the protective device will still operate in the required time with the smaller ground, in reality, unless you have a very long circuit it works just fine.

Are you using 1.5 for outlets? If so you must use a 16A breaker.

[topher]

Are you using 1.5 for outlets? If so you must use a 16A breaker.

Yes, and yes 16A for outlets and 10A for the lights circuits (fluorescents). It's a small house.

4 x 16A outlets (BRs, LR, Kitchen, Outdoor) and 4 x 10A for 2 lights circuits, 1 water pump and 1 very small aircon (4A rating) in my bedroom.

Keep in mind we're on a typical Issan 5A meter (for now)! (ha ha). The word around here is you'll be lucky if they ever allow more than that. Some locals have requested 15A and not had it upgraded even after several years.

Longest circuit in house is in range 7-9m and there is one longer one going out to the water pump but it should be pulling about 5A or so (intermittently).

Edited March 23, 2012 by topher

[electau]

Earthing conductor size is based on the cross sectional area of the largest active conductor supplying the portion of the electrical installation to be protected.

With the exception of the main earthing conductor and bonding conductor, 2.5sqmm is the max that is required in the average electrical installation.

RCDs have nothing to do with size of earthing conductor, they will operate without an earth conductor in the event of a earth fault.

Earth conductors only carry current while an earth fault exists, the protective device clears the fault. The fault must be cleared quickly to prevent undue temperature rise in the cable.

2.5sqmm copper has a resistance of 0.008ohms per metre.

1.0, 1.5sqmm copper can be used as earth conductors provided they are laid up in the same sheath as the current carrying conductors. Otherwise the minumum is 2.5sqmm.

[bankruatsteve]

1.0, 1.5sqmm copper can be used as earth conductors provided they are laid up in the same sheath as the current carrying conductors. Otherwise the minumum is 2.5sqmm.

Why is the minimum required larger if not in (I think you're saying) 3 core PVC (or ROMEX as we call it in the states)?

[electau]

1.0, 1.5sqmm copper can be used as earth conductors provided they are laid up in the same sheath as the current carrying conductors. Otherwise the minumum is 2.5sqmm.

Why is the minimum required larger if not in (I think you're saying) 3 core PVC (or ROMEX as we call it in the states)?

These sizes are stipulated in AS/NZ 3000. What is known as Romex in the US is in Australia known as 2core + earth PVC insulated, PVC sheathed, or TPS insulated and sheathed cable.

2 core and earth, 3 core and earth, 4 core and earth.

Where an earth is run as a separate conductor the minimum size is 2.5sqmm (7/.067)

　

　

　

　

　

　

Edited March 27, 2012 by electau

[topher]

I was just reading thru the US Code (Oregon 2011 version). I see table 250.122 which defines 14 AWG as the minimum ground conductor size. That would be 2.5mm here. But then I see this wording just ahead of that, same section,

"equipment grounding conductors of the wire

type shall not be smaller than shown in Table 250.122,

but in no case shall they be required to be larger than the

circuit conductors supplying the equipment."

(emphasis mine)

This seems to indicate a basis for not having the ground conductor larger than the load conductors. In the US Code the load conductor minimum for an outlet circuit appears to be 14 AWG so I think Table 250.122 corresponds. But here, a 16A outlet circuit is allowable using a 1.5mm conductor (unless I'm wrong I see that in the guide I have here) and it would seem to follow that a 1.5mm ground conductor would be sufficient.

But I also see in that US Code that running a single 14 AWG Ground conductor in a raceway supporting multiple load conductors is sanctioned as long as it is as large as the largest load conductor.

I guess I'm grasping at straws here as the Romex type 1.5x2/1 wire is so pricey here, and using 2.5mm grounds everywhere would also be quite costly. I could see running one main 2.5mm down the raceway but baulk at running (6 circuits) multiple 2.5mm grounds, or 6 separate 2x1.5/1 circuits. Even if I accept that 14 AWG (2.5mm) is the minimum (even with load condutors of 1.5mm) then I would definitely want to run one main ground and branch off that.

Also, I had a look at terminal strips for making branch ground connections in the raceway and they seem a bit fiddly since you would have to insert 2 conductors into screw joints to branch off the main. Small busbars would be better since that would have one screw per wire but I haven't seen those available (like a 3-4 screw bar). So I think I'd prefer soldering grounds and capping with a wire nut if that is an acceptably secure connection.

[bankruatsteve]

When comparing wire size between USA and places using 220v, remember that the wire can be much less cross section with 220v to supply the same load in 110v.

[Crossy]

There is nothing electrically wrong with running a ground buss and using droppers to the points of usage. It would not be permitted in the UK or Aus where each circuit must have its own ground back to the Main Earth Terminal (MET). If you do choose to use a buss I would make it 2.5mm2, use 1.5mm2 droppers if you wish. I would also run individual ground line for high current devices, water heaters, aircon, range etc.

Consider using Scotchlok IDC connectors to attach your droppers, the ones readily available are intended for automotive use (rated at 30V) but since the ground wire should remain near, well, ground, I see absolutely no reason not to use them and they are cheap and fast. They also have the advantage that you don't need to cut your buss wire so the danger of accidental disconnection is reduced.

Do NOT use Scotchloks for the L and N connections unless you can source the 600V versions which I've not seen in Thailand.

EDIT Evidently my brain is in fade mode today, I said most of that in a previous post

[topher]

I'm guessing you mean these, rated for 600V and 0.75mm - 1.5mm. ScotchLok 567 series.

http://www.shop3m.co...tml?WT.z_bynt=1

I'll see if they're available here as they would be quite easy to use. Maybe I can find similar cable clamps that use a screw to bind two parallel cables.

I think my current plan is 2.5mm main buss and 1.5mm drops for outlets, 1mm drops for lights. These drops match load conductors.

Edited March 29, 2012 by topher

[Crossy]

Yup, those are the 600V ones.

The automotive (30V) ones are readily available and will be just fine on the ground conductor. Talk to places installing car audio and lighting.

[topher]

According to the US code it's ok to run a bare ground wire in a raceway. I was thinking of doing that for the main trunk and then for the branch drops twisting a green wire (to the main bare line) and soldering it . This would be quite easy (as I've done a lot of soldering before) and secure from coming loose. Comments?

[Crossy]

The only place I've seen bare copper earth permitted in raceway / conduit is in India. It's certainly not permitted in the UK and chances are not in Australia.

Personally I wouldn't do it even if not specifically prohibited, the danger of it touching something live is too great. If you want to pigtail and solder strip the insulation off a short section with a knife (no need to cut the conductor), solder your dropper, and tape.

[topher]

The only place I've seen bare copper earth permitted in raceway / conduit is in India. It's certainly not permitted in the UK and chances are not in Australia.

Personally I wouldn't do it even if not specifically prohibited, the danger of it touching something live is too great. If you want to pigtail and solder strip the insulation off a short section with a knife (no need to cut the conductor), solder your dropper, and tape.

Ok, will shelve that idea. I'll probably dig up the ScotchLok connectors then. Thanks.

[electau]

The only place I've seen bare copper earth permitted in raceway / conduit is in India. It's certainly not permitted in the UK and chances are not in Australia.

Personally I wouldn't do it even if not specifically prohibited, the danger of it touching something live is too great. If you want to pigtail and solder strip the insulation off a short section with a knife (no need to cut the conductor), solder your dropper, and tape.

Bare copper stranded conductor was used up to 1961, after that earthing conductors had to be insulated with sleeving behind fittings and in switchboards, after 1976 earth green or green /yellow insulated conductors were made mandatory under the AS Wiring Rules.