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Old 08-30-2016, 11:55 AM   #1
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Default Bonding a resi furnace

With a typical residential natural gas fired hot water furnace with a 120V feed, is it ok to bond the furnace simply by solidly screwing the electrical box to the metal furnace body?

ETA: Also there will be chase nipple connecting the box to the furnace.

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Old 08-30-2016, 11:58 AM   #2
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Off hand I can think of a reason not to. Bonding connections can serve no other purpose than bonding. Maybe screw the box on and then add another screw (that you have to colour green somehow) and claim it's only for bonding.

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Old 08-30-2016, 12:02 PM   #3
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With a typical residential natural gas fired hot water furnace with a 120V feed, is it ok to bond the furnace simply by solidly screwing the electrical box to the metal furnace body?

ETA: Also there will be chase nipple connecting the box to the furnace.
With new HSI and spark ignition systems the biggest cause of problems with a furnace lockouts is improper or poor grounding. Check the installation specs as there should be a small section regarding this.
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Old 08-30-2016, 09:22 PM   #4
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With a typical residential natural gas fired hot water furnace with a 120V feed, is it ok to bond the furnace simply by solidly screwing the electrical box to the metal furnace body?

ETA: Also there will be chase nipple connecting the box to the furnace.
Have to be careful not covering nameplate etc,

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Old 08-30-2016, 09:41 PM   #5
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Any I've wired had integral wiring box with integral bonding screw
or grn insulated bonding tail. Bout the same as a D/W. Shouldn't
they all?
P&L
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Old 08-30-2016, 10:48 PM   #6
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Any I've wired had integral wiring box with integral bonding screw
or grn insulated bonding tail. Bout the same as a D/W. Shouldn't
they all?
P&L
Depends, Weil McLain gives you a bag of parts and you supply the finesse in wiring. Some of the wall mounted boilers are much moire advanced.
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Old 08-31-2016, 06:36 AM   #7
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Depends, Weil McLain gives you a bag of parts and you supply the finesse in wiring. Some of the wall mounted boilers are much moire advanced.
Cast iron weil mclains don't count the whole damn thing has to be put together in the field.
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Old 08-31-2016, 08:22 AM   #8
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If it is in conduit the entire way I don't see a problem with it. Probably can't use self tappers though. I would probably run a jumper from the box to the furnace ground screw.
Most of the time I just run a romex and sleeve it down to the furnace in EMT. If there is no ground or anything unrelated to the furnace is on the same circuit it gets a new circuit.
Have done 3 already this week haxer...
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Old 08-31-2016, 08:48 AM   #9
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If it is in conduit the entire way I don't see a problem with it. Probably can't use self tappers though. I would probably run a jumper from the box to the furnace ground screw.
Most of the time I just run a romex and sleeve it down to the furnace in EMT. If there is no ground or anything unrelated to the furnace is on the same circuit it gets a new circuit.
Have done 3 already this week haxer...
You need an actual ground wire for any with advanced controls to work properly. Especially those with flame rectification.
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Old 08-31-2016, 09:24 AM   #10
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You need an actual ground wire for any with advanced controls to work properly. Especially those with flame rectification.
I thought that conduit was actually a better ground than a copper wire. Now I gotta go look for that study.
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Old 08-31-2016, 09:38 AM   #11
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I thought that conduit was actually a better ground than a copper wire. Now I gotta go look for that study.
The study could be great to lab experiments but in the field, I've seen this problem countless times. "Intermittent ignition faults" have been a constant heating problem since the ignition systems using flame rectification have become popular. It can work a hundred times and then lock out leaving you without heat until someone comes and resets the power and themodule tries again, an works the next 95 times.

The following is from a fast google search. Similar articles can be found on all hvac sites and the vast majority are all 'ground' quality related.

IGNITION SYSTEM GROUNDING
Nuisance shut downs or no operation at all can be caused by a poor or
erratic ground connection.
1. From the ground (GND), usually green wire, terminal on the
module check for continuity to some portion of the boiler or
furnace. It is best to check on an unpainted and clean surface. The
gas pipe is a good point. YOU SHOULD HAYE CONTINUITY! !
Ifyou do not then you could experience erratic or no operation at
all.
a. It may be necessary to establish a good connection to
ground by using a wire with a clamp onto the gas line or
equipment chassis and connecting it to the ground terminal
of the module. All connections should be clean, unpainted
and good metal-to-metal contact. When you look at the
wiring diagram for the equipment and see this type of
symbol showing the use of a chassis ground be careful that
you have a good connection.

"Re: Carrier Ignition Lockout
Be sure that the furnace is grounded properly. The control board sends current through the flame sensor, which goes through the flame and then to ground. If the board is not grounded, the circuit will not be complete, and it will not know that the flame is lit and shut off the gas, causing a lockout."
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Old 08-31-2016, 10:02 AM   #12
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I thought that conduit was actually a better ground than a copper wire. Now I gotta go look for that study.
In actual use I've never seen this to be the case. With the exception of rigid there's just too many shoddy splices in conduit. They may start out nice and tight but a couple dozen heat cycles later and maybe a little moisture for corrosion and the conduit system just isn't worth while as a ground. Mostly what I've seen is a few good clamps holding the conduit to grounded building metal closer to the device is what's making the ground. Anyone that's done service for awhile has seen plenty of conduit systems that have been pulled completely apart with only the conductor holding it up. Conduit as ground might look fine from an installers point of view but long term it's a bad call.

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Old 08-31-2016, 11:42 AM   #13
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I don't know if the furnace came wired or if the plumber/HVAC guy did it.

The furnace had a 1900 box inside of it held to the body with an MC connector used as a nipple. A black and white wire were sticking out thru the MC connector. When I opened the 1900 box I found a ground clip on it. The black and white wire were coming directly from the transformer mounted to the 1900.

I removed the MC connector and used a chase nipple to hold a handybox to the outside and the 1900 inside. I also ran some zippies thru the boxes to hold them tighter.

I ran MC cable then sleeved it in EMT down to the handy box. I ran the MC's ground around a ground screw in the handybox, thru the nipple into the 1900, and then terminated it under the ground clip.

I wired the whites and the blacks up to the tranny and left.

So that's my concern, the ground ends at the boxes which are bonded to the body. But I didn't see any other ground lug or screw anywhere else.
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Old 08-31-2016, 11:46 AM   #14
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I don't know if the furnace came wired or if the plumber/HVAC guy did it.

The furnace had a 1900 box inside of it held to the body with an MC connector used as a nipple. A black and white wire were sticking out thru the MC connector. When I opened the 1900 box I found a ground clip on it. The black and white wire were coming directly from the transformer mounted to the 1900.

I removed the MC connector and used a chase nipple to hold a handybox to the outside and the 1900 inside. I also ran some zippies thru the boxes to hold them tighter.

I ran MC cable then sleeved it in EMT down to the handy box. I ran the MC's ground around a ground screw in the handybox, thru the nipple into the 1900, and then terminated it under the ground clip.

I wired the whites and the blacks up to the tranny and left.

So that's my concern, the ground ends at the boxes which are bonded to the body. But I didn't see any other ground lug or screw anywhere else.
Sounds like you're good.
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Old 08-31-2016, 11:57 AM   #15
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Originally Posted by HackWork View Post
I don't know if the furnace came wired or if the plumber/HVAC guy did it.

The furnace had a 1900 box inside of it held to the body with an MC connector used as a nipple. A black and white wire were sticking out thru the MC connector. When I opened the 1900 box I found a ground clip on it. The black and white wire were coming directly from the transformer mounted to the 1900.

I removed the MC connector and used a chase nipple to hold a handybox to the outside and the 1900 inside. I also ran some zippies thru the boxes to hold them tighter.

I ran MC cable then sleeved it in EMT down to the handy box. I ran the MC's ground around a ground screw in the handybox, thru the nipple into the 1900, and then terminated it under the ground clip.

I wired the whites and the blacks up to the tranny and left.

So that's my concern, the ground ends at the boxes which are bonded to the body. But I didn't see any other ground lug or screw anywhere else.
Sounds like you are bonded with listed means. I personally don't trust ground clips but since they are listed...You are legal.

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