Upgrading Vent Hood: Can 2nd Neutral Be Used as a Ground?

Reply

  #1  
Old 09-06-15, 10:23 AM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
Upgrading Vent Hood: Can 2nd Neutral Be Used as a Ground?

We've been redoing our 1959 Ohio kitchen for quite some time. We are almost done, and are on the range hood. We removed the old hood, and there were three wires coming from it. We couldn't get into the old hood, so we snipped them off. One wire is black, and two are white. Would the whites both be neutral? Would there be one neutral to run the fan and one to run the lights, or was one used as a ground?

Two main things I'd like to know:

1. Can I tell the difference between the two white wires in case one was ground and the other neutral?

2. Does that even matter? Can I use a neutral wire as the ground and a neutral for neutral? There are other things hooked up on this circuit if that matters - outlets and light switches.

Thanks for any help.
 
Sponsored Links
  #2  
Old 09-06-15, 10:28 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
Welcome to the forums.

You cannot use a white, possibly a neutral wire, as a ground.
Having two white wires and one black wire doesn't make much sense.
Is this wiring in conduit ?
 
  #3  
Old 09-06-15, 10:36 AM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
No conduit. Each wire was individually insulated with some sort of soft thick black insulation. Is there any way to tell if one is actually ground?
 
  #4  
Old 09-06-15, 10:38 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
There has to be a common jacket. You can't just have three wires laying in the wall.

No... there is no way to check that wire for ground other than finding where that wiring is connected and checking there by opening the connections and using an ohmmeter.
 
  #5  
Old 09-06-15, 10:43 AM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
Unfortunately, we have three wires laying in the wall. They come from the attic. I don't know if I can physically get to the edge of the house in the attic with the roof still intact.

Say I find where they are connected and I have an ohmmeter - what's the difference between neutral and ground?
 
  #6  
Old 09-06-15, 10:56 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
Neutral and ground will check out exactly the same. They are ultimately connected together BUT only at the panel.

Since they will check out the same there is no way of ID'ing them other then at their source.
 
  #7  
Old 09-06-15, 11:04 AM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
After a trip into the attic, that seems impossible to track back... I can't even get to a place where I can see where they come up into the attic. I know which breaker they're connected to. I don't suppose there is a way for me to send a signal at the breaker through one of the white wires that I would be able to read at the fan end? Just grasping at straws here, otherwise I suppose I will need to hire an electrician to run a new line from the basement.
 
  #8  
Old 09-06-15, 11:27 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
Do you have knob and tube?
Each wire was individually insulated with some sort of soft thick black insulation.
That sounds like loom on K&T wires where they enter the box.

Name:  knob_and_tube.jpg
Views: 539
Size:  10.5 KB
Source: inthebeach.com
 
  #9  
Old 09-06-15, 12:06 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
There are K&T wires in the attic. I can't see the particular wires that are feeding these three black wires. They are not at the box of course, they are going to the fan. All separate with thick black insulation.
 
  #10  
Old 09-06-15, 12:29 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
K&T is somewhat unusual for a house built in '59. Do you have a multimeter, preferably analog? Do you have known good receptacle with ground? If so you can test the wires easily using an extension cord with ground.
 
  #11  
Old 09-06-15, 12:44 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
None of the receptacles attached to this breaker have ground.
 
  #12  
Old 09-06-15, 01:31 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
Just a receptacle anywhere in the house.
 
  #13  
Old 09-06-15, 03:26 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
I definitely have some of those.
 
  #14  
Old 09-06-15, 03:38 PM
Member
Join Date: Sep 2015
Location: Canada
Posts: 8
Can be vs. Should be

If both the white wires are 0V to ground (connected to ground or neutral) and both are insulated wires continuous to the panel, there is no electrical difference and either 'Can be' used. The 'should be' aspect comes in with the Electrical code.
 
  #15  
Old 09-06-15, 03:40 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
K and T is certainly unexpected in a house of that vintage.

I would imagine that you will end up combining the two white wires together as the neutral and black to the black. There is no ground run.

I'm not sure where Ray is going so I'll let him handle that.
 
  #16  
Old 09-06-15, 04:11 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
I can't guarantee the wires are continuous to the panel. Can that be the case when there are other items on the same breaker? I just know there are 3 wires going up to the attic. I can't see those specific wires in the attic, but I can see K&T wires in the attic.

I guarantee the vent hood was in the house from the start, but we didn't buy it until 1997. There was an attached garage added in the late 80's or so, and that's on the wall the vent hood is on, so there could have been an electrical update to that area. I don't know why anyone would go out of their way to update the wiring to this hood as it would be a real pain to get to from what I can see.

Why would the old hood have 2 neutrals connected to it?

There is a new outlet for the gas cooktop beneath the counter on that wall, and it has a ground. Could the ground from that circuit be routed to this hood above it?
 
  #17  
Old 09-06-15, 04:47 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
Could the ground from that circuit be routed to this hood above it?
No. If you run a ground to it it must come from the panel.

Since you have a receptacle below the hood you can use it as the reference for your testing. First test the receptacle is wired correctly and has a ground by measuring from the ground hole to the narrow slot of the receptacle. If you get ~120 volts you are good to go.

Plug an extension cord with a ground into it. Measure the voltage from the narrow slot of the extension cord to each of the white wires at the vent. Tell us the readings.
 
  #18  
Old 09-06-15, 06:37 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
Ok, I connected the ground and the narrow slots of the receptacle, and sure enough, there were 120V. I then connected an extension cord to the outlet. I connected the ground of the extension cord to each of the white wires, and came up with 0 in both cases. I also connected the narrow slot of the cord to the white wires, and got 120V both times. Hopefully that's not hurting anything, I just wanted to make sure I was connecting properly.
 
  #19  
Old 09-06-15, 06:45 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
This is a head scratchier. I would be tempted to use only one neutral and cap the other but PJ says use both and he is the pro. I think though he was thinking that one wire carried the neutral elsewhere. In that case only one neutral would show voltage. Wait for PJ. I'd probably just run a new cable and cap all the old wires since there is no ground. (Neither white can safely be used as a ground.)
 
  #20  
Old 09-06-15, 06:53 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
Use one and cap off the other. It would appear that the second white may have been used as a ground wire.
 
  #21  
Old 09-06-15, 07:52 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
So does that mean no ground is needed? None of these options are using a ground of any kind.
 
  #22  
Old 09-06-15, 08:11 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
That is a dicey issue. Yes.... technically a ground is needed. A ground is needed in case something in the hood shorts to the metal case. With a ground connection..... that short would trip a breaker or blow a fuse.

Without a ground the case could potentially become live.
If you were to use the white wire as ground and the neutral opened..... the case would become live.

The only place to get a proper ground is from the panel.
 
  #23  
Old 09-06-15, 08:13 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
How hard would it be to run a new cable? Do you have an unfinished attic above or basement below. Is the wall the vent hood is on an outside wall or inside wall?

Since you say you can't get to the place they come up we will rule that out for now.

If a basement below you can come up from the basement. If an outside wall you can run conduit or even buried cable to the area of the vent hood. I doubt an inside wall since you say you can't get to it from above. Another possibility is running wiring through the cabinets from an assessable point to the fan.

There is one other safety issue that bothers me. Is there attic insulation in the area where the K&T goes down to the vent hood? That would be a hazard. K&T should be in free air not covered with insulation. Another reason to abandon that K&T.
 
  #24  
Old 09-07-15, 07:31 AM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
Thanks for all the help and knowledge, it's much more reassuring than my general ignorance.

I haven't run anything since we had an electrical section in wood shop 25 years ago, so it's not really my forte - I definitely don't know any of the code. The box is in the basement on the other side of the house. It is an unfinished basement, although the trip up through the cabinets is still a little tricky. We'll have to uninstall our oven. There are questions still eating at me though:

1. Would there be any reason why a vent hood would need 2 neutrals in 1959? It's a Nutone range. We are replacing with a Broan/Nutone, and it calls for 3 wires, hot, neutral, and ground. Why would the old one have been different?

2. I'm guessing one of these white wires must be ground. Is there a way for me to test them by powering up the other switches on the breaker to see which one is neutral and which isn't? I don't want the hood to become live, but in 54 years that didn't seem to happen.

3. I'm also perplexed as to why a ground wire from one circuit isn't as good as the next. I didn't think every ground wire in the house was connected directly to the box. There are junction boxes - can't the ground be split in one of those into 2 wires?
 
  #25  
Old 09-07-15, 08:40 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
Would there be any reason why a vent hood would need 2 neutrals in 1959?
No.
Why would the old one have been different?
It wasn't. Most likely someone with just enough knowledge to be dangerous ran an unsafe bootleg ground.
Is there a way for me to test them by powering up the other switches on the breaker to see which one is neutral and which isn't?
Code says a white can't be used as a ground.
There are junction boxes - can't the ground be split in one of those into 2 wires?
Code allows you to run just a ground to it but it must be connected to the main ground within five feet of the panel. It can not come from a branch circuit ground. If you think running a single green wire (#14 THHN/THWN green) would be easier than a new cable you can do that.
 
  #26  
Old 09-07-15, 05:26 PM
Member
Join Date: Sep 2015
Location: Canada
Posts: 8
Safe vs. Code

[Unsafe advice removed. Original archived.]

One other thought on the testing... Since you know the circuit at the panel, you should be able too identify the White that enters the panel with the black for that circuit. Disconnect the circuit and then remove that white wire from the neutral bus. With the panel end of that wire in air, a measurement across the hot (narrow slot) of that extension cord and the 2 white wires at the hood fan should identify which is connected to the white wire you disconnected at the panel. That will be your Neutral at the hood fan.

Mod note: That might work if the wire originates at the panel but it may originate at a branch circuit.

Be sure to ground the hood fan one way or another and it'll be safe. That's the important thing! ;-)
Mod note: Not one way or the other. You should use only a code aproved method.
 

Last edited by ray2047; 09-07-15 at 05:47 PM.
  #27  
Old 09-09-15, 11:04 PM
Member
Join Date: Sep 2015
Location: Canada
Posts: 8
"Safe" and "by Code" are not synonymous.
 
  #28  
Old 09-09-15, 11:09 PM
Member
Join Date: Sep 2015
Location: Canada
Posts: 8
All neutral runs originate at the panel. Even when branched, removing the connection at the panel would break the circuit.
 
  #29  
Old 09-09-15, 11:26 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
Lakeman..... you do realize that we are dealing with knob and tube wiring..... right ?
There are only two wires run..... hot and neutral. NO ground.
 
  #30  
Old 09-10-15, 06:31 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
Even when branched, removing the connection at the panel would break the circuit
And every other device or fixture relying on that neutral. Capping at the fan is the only way that makes sense in this situation.
 
  #31  
Old 09-12-15, 04:02 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
There are three wires though, two are theoretically neutral.
 
  #32  
Old 09-12-15, 04:10 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
Related: I have a question about code. I'm still wondering if I should just run a green wire for ground from the box, or just a whole other cable.

I was looking at the work the last electrician did. He ran one circuit for an outlet for our dishwasher/disposal, and another circuit for an outlet for our gas range and gas oven. From the box he used white cables for each (are these romex?), and they lead into a junction box under the kitchen. Each circuit breaks off there, but they come out housed in flexible metal conduit.

Why not just run the white cables all the way to their destinations? Why the junction box and metal conduit? Is that a special precaution since the wiring is going into the cabinets?
 
  #33  
Old 09-12-15, 04:47 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
'm still wondering if I should just run a green wire for ground from the box, or just a whole other cable.
Either is code compliant. Usually just whatever is easier but since you have K&T I'd say cable. If you have insulation in the attic then it is very important to use cable because K&T must be in free air for cooling not under insulation.
From the box he used white cables for each (are these romex?), and they lead into a junction box under the kitchen
Yes, it is NM cable. (Can't say if it the Romex brand.)
Each circuit breaks off there, but they come out housed in flexible metal conduit.
Or is it flexible metallic conduit? Either is okay. Do you have grounds.
Why not just run the white cables all the way to their destinations?
Protection maybe.
 
  #34  
Old 09-12-15, 04:48 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,511
White wire sounds like NM-B (romex) cable. He may be using old stock up as #12 NM-B for 20A kitchen circuits is now yellow.... and has been for a good many years.

Running a metal clad type cable is usually done for protection although a lot of old timers still use it in residential work.


wow....Ray is fast
 
  #35  
Old 09-12-15, 06:46 PM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
Both of the new circuits have grounds. My box is a GE TM20DC. It has 4 screws on the front I assume I need to remove to get into it - I suppose I have to turn the main power off before opening it up, or do I just need to switch off the breaker I'm going to be messing around with? I'm used to using LOTO at work, not for electrical work, but when I'm cleaning machinery and whatnot.

EDIT: PS the two new circuits are on yellow cables. Dim light, light yellow.
 
  #36  
Old 09-12-15, 08:12 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
I suppose I have to turn the main power off before opening it up
That is best practice if you aren't use to working in the box.
 
  #37  
Old 09-13-15, 07:38 AM
Member
Thread Starter
Join Date: Sep 2015
Location: USA
Posts: 15
It appears as though it's ok for me to use an open 15 amp breaker on my box to power this vent hood. It looks like I could use 14-2 NMB with ground - is that ok to run directly through kitchen cabinets without protection? I'm sure it will be absolutely fine, but it's also up to code? Some places I'm reading NMB cable should be covered by sheet rock or be in an area where there's little chance of access like a crawlspace.
 
  #38  
Old 09-13-15, 09:51 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,675
It looks like I could use 14-2 NMB with ground - is that ok to run directly through kitchen cabinets without protection?
If running horizontally run it as close to the bottom of the cabinet top as possible. You might want to sleeve it in flexible non metallic conduit on vertical runs.

Name:  2121404632_c0b2289176_o.jpg
Views: 142
Size:  7.0 KB Name:  5d33d73b-c965-487d-abc5-2c3bc56aab44_1000.jpg
Views: 173
Size:  8.5 KB
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'