Grounding

Alan (California Radiant) Forbes

Why do I never see a hot water or steam system grounded? Surely, a hot wire in a wall can work loose and electrify a pipe and endanger the occupants?

EBEBRATT-Ed

The hot water or steam system (warm air too) is considered grounded by the circuit feeding the boiler or furnace. This may be a 15 or 20 amp 120 volt circuit in most cases. The ground can consist of a green or bare equipment ground run with the circuit conductors. Or the ground can be through the emt, ridged conduit, or other metal raceway correctly installed. In many cases with older systems even if the burner is grounded by the electrical circuit the boiler may not be (older floor mounted burners)

Although the National Electric Code does not consider this as a ground most boilers are connected to a water pipe usually metal which is grounded at the electric service. The code requires the gas piping to be grounded but this is subject to local inturpratation

The general rule is anything metal is supposed to be grounded if it is fixed in place older systems may not have caught up yet.

There are cases where stainless steel sinks feed by plastic pipes and inspectors have made the electrician ground the sinks. Believe it or not "swimming pool" water has to be grounded

ChrisJ

I agree with @EBEBRATT-Ed

But, what does amaze me is aluminum siding isn't required to be grounded.

EBEBRATT-Ed

@ChrisJ
I have herd (never done it) that aluminum siding is supposed to have jumper put on around the corners of the house.

Another case of "accidental grounding" I guess. Light fixtures attached to it, outside outlets, meter socket??

HomerJSmith

Alan, perhaps you're not looking close enough. Everything that I see has a ground bonding screw except a W/H. The only grounding that I see on a gas line is for CSST. The thing is, you could have a 20 amp circuit breaker and have a leak to ground of 15 amps and never trip the breaker. I have checked the appliance with a meter for AC voltage (zero) to a good electric ground and also checked the ohms for zero.

JUGHNE

If that 20 amp circuit was draining 15 amps into grounded/bonding piping, then the piping would not be a threat of electrocution. IMO.

Hard to stay at the 15 amps without the leak becoming a dead short and then tripping the CB, but I get your point. Usually it would be a small current flow that would be dissipated by the bonding system.

Some where in the National Electric Code (the book of exceptions BTY) it states that any metallic objects, be it piping of any sort, ductwork (isolated by canvas connectors even) shall be bonded with grounding wires sized to handle the largest circuit available in that area. Think of the electric range circuit of 60 amps as being the perhaps largest circuit in a house.
Electric WH tanks are grounded by the circuit wiring. Gas WH bonded/grounded by the gas piping. Both may have insulating dielectric plumbing fittings installed so the water piping, H&C, needs separate bonding.
Number 6 copper will bond up to 200amps.
Number 4 copper will ground up to 200 amps.

HomerJSmith

"If that 20 amp circuit was draining 15 amps into grounded/bonding piping, then the piping would not be a threat of electrocution."--unless you provide a better ground thu your body.

EBEBRATT-Ed

If a 20 amp circuit is putting 15 amps to ground you would have no problem because the house would have already burnt to the ground.

@JUGHNE

I believe the code say something like " metal that may become energized should be grounded in accordance with the size of the circuit likely to energize it". So no need to ground everything to 60amps

JUGHNE

Ed, as I am sure you know, you do what the AHJ wants.
I had an inspector, that if the range wire ran the length of the house parallel to the piping, then we talk 60 amp bonding. Maybe #10 copper.
If a machinal room with only 20 amp circuits then #12 would suffice.

EBEBRATT-Ed

@jughne,

I don't like arguing with inspectors but I have no problem beating them over the head with a code book nicely when they are wrong.
I find most all of them have been pretty reasonable with me over the years, but you have to know the code. They will often back down when they find out your reading the code book.

Not that I am as up to date as I should be

Jamie Hall

I quite agree with @EBEBRATT-Ed -- and in the bad old days when I was doing inspections I always welcomed a knowledgeable contractor who knew the code and could help me understand it. Not to say all inspectors do...

On the other hand... in some situations -- particularly if one is playing with gas or other flammables -- going slightly overboard on bonding (and grounding) isn't likely to hurt. Reason being that in some situations remarkably high voltages can be induced in pipes or other conductors by high current parallel wires (particularly if there are switching transients -- think contactors on big motors). Will this have enough energy to create a spark with enough energy to light off a leak? Don't know. Don't want to find out, either...

Solid_Fuel_Man

Another good reason to avoid the glorified appliance connector knows as CCST! Gotta run a bonding conductor sized to ??? I do feel sorry for the natural gas guys who can't run soft copper though. Black iron sometimes doesn't lend itself well to old construction without opening things up. Using a material with excellent current carrying capabilities (copper or large steel pipe) is good safety.

As far as grounding goes, all equipment I've installed has a ground screw/lug. The grounding conductor is sized per 2017 NEC 250.122. As a rule on #10 or smaller a full size (same size as current carrying conductors) is used. On circuits #8 and larger the table is used and a suprisingly small conductor can be used.

The grounding conductor is sized so that if a bolted short to ground happens (dead short) a "reasonable" voltage drop happens and the over current device opens.

I've never had to deal with sizing the grounding conductor to the largest circuit in a place, seems kinda ridiculous.

Jamie Hall

The smaller wire comment is good -- actually a small amount of resistance in the ground circuit is a good thing, oddly enough (although there is usually ample resistance for electricians not to have to worry about it). The resistance serves to reduce "ringing" and dismayingly high voltage spikes if a high voltage dead short occurs. It's a good tip for discharging large or high voltage capacitors, too -- it's better to discharge them by shorting with a 10 to 100 ohm resistor than it is to discharge with a dead short.

EBEBRATT-Ed

15 amp circuit=#14 ground. 20 amp circuit=#12 ground. #10 ground is good for up to a 60 amp circuit. #8 for a 100 amp circuit. Higher than that I would have to look it up.

Keep in mind that the ground can also be emt, ridged conduit, greenfield or sealtight etc.etc. under certain conditions

ChrisJ

Jamie Hall said:

The smaller wire comment is good -- actually a small amount of resistance in the ground circuit is a good thing, oddly enough (although there is usually ample resistance for electricians not to have to worry about it). The resistance serves to reduce "ringing" and dismayingly high voltage spikes if a high voltage dead short occurs. It's a good tip for discharging large or high voltage capacitors, too -- it's better to discharge them by shorting with a 10 to 100 ohm resistor than it is to discharge with a dead short.

Is this the Twlight Zone?

Ringing?

Jamie, are you feeling ok?

Jamie Hall

Actually, I'm feeling fine... the reasoning is this: if there is even a small amount of inductance in whatever circuit is involved when you are trying to discharge a large or high voltage capacitor, the circuit will oscillate rather than discharge, unless there is some resistance to dissipate the energy. Which is what I meant when I referred to "ringing". Most of the capacitors we play with aren't big enough to be a problem, but the power factor compensating ones on industrial equipment are -- and so are the power supply capacitors in high fidelity power amplifies. So are cathode ray tubes (the capacity there isn't much -- it's just the plate -- but at 20,000 volts...)

For equipment grounds, you don't want that much resistance -- you can figure the actual maximum allowable resistance if you want to (for instance, 8 oms for a 15 amp circuit, 6 for 20, 4 for 30 -- all assuming 120 volts to ground) but why bother? Code has you covered on that.

ChrisJ

Jamie Hall said:

Actually, I'm feeling fine... the reasoning is this: if there is even a small amount of inductance in whatever circuit is involved when you are trying to discharge a large or high voltage capacitor, the circuit will oscillate rather than discharge, unless there is some resistance to dissipate the energy. Which is what I meant when I referred to "ringing". Most of the capacitors we play with aren't big enough to be a problem, but the power factor compensating ones on industrial equipment are -- and so are the power supply capacitors in high fidelity power amplifies. So are cathode ray tubes (the capacity there isn't much -- it's just the plate -- but at 20,000 volts...)

For equipment grounds, you don't want that much resistance -- you can figure the actual maximum allowable resistance if you want to (for instance, 8 oms for a 15 amp circuit, 6 for 20, 4 for 30 -- all assuming 120 volts to ground) but why bother? Code has you covered on that.

Understood.

However when it comes to equipment grounding I thought it all came down trying to maintain as low of resistance as possible vs cost.

Jamie Hall

True. I went off on a tangent. What else is new?

nibs

Thought grounding was what they did in California to set their karma straight.

Alan (California Radiant) Forbes

Lots of crooked karma out here.

Larry Weingarten

The Golden State Rule: “Do unto others.”
Yours, Larry

Jamie Hall

My karma ran over my dogma...

Larry Weingarten

Ok, Just to stay off topic a bit more, it's fortunate that we don't all, always follow the rules @Jamie Hall , poor dogma!

Yours, Larry