We have a bakery oven at a grocery store that wouldn't turn on. It's a 240v 3 phase oven and one leg is used to get 120v for the control circuit. We were measuring voltage between neutral and ground, about 45v. If we used a jumper wire from neutral to ground everything worked fine. Called an electrician in to run a new neutral wire after isolating every circuit on the oven and finding nothing wrong with any component. The electrician ran a new neutral but said it still has issues. At this point I'm wondering if we need a different company to have a look. I suspect something with the load center but my license is only for equipment so it's beyond my scope.
Neutral issue on commercial oven
- Thread starter Williehbt
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hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Then there it is most likely a bad neutral. How did the electrician run a new neutral and did he test it? Could be a bad neutral in the panel where the circuit originates so running a new neutral solved nothing.
That's what I was wondering about
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
It would be unusual for a grocery store to have 240 volt three phase, unless it’s small like a convenience store. if it does you would have a high leg, and if the 120 volt controls were on the wrong leg, it would let the magic smoke out. It should be 120/208. But if it is an actual 240 volt three phase panel, it may have a neutral bar in it, but not connected to the neutral. That is why you have 120 to ground, but not the neutral. The installing electrician should have removed it, and labeled the panel, but that doesn’t always happens! Are there any single pole breakers in that panel?
- Location
- Illinois
- Occupation
- retired electrician
Could be a missing main bonding jumper if the only path between the utility grounding electrode and the building is the earth.
Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
Some old store have a six wire.
In the three phase panle generally there is no netural. 240 volt only with a EGC. The MBJ is attached to the elclouseur and an GEC is ran to the electrode from that point
Then the netural is in the single phase panle.
A sign of this would be two panels sitting side by side one three phase and one single phase. Or a wire way with the two panels sitting above it.
When we read 240 three phase it generally leads to more questions.
Just throwing out another option of why.
Old store use the three phase for compresses and such. The rest single phase.
A few pics of electrical equipment might help. Also if over head service you will have two drops for a six wire or taped at the weather head to a single four wire drop.
Also talk with your electrician and ask what he attached the netural to in the panle.
It amazing what a voltage sticker can solve.
In the three phase panle generally there is no netural. 240 volt only with a EGC. The MBJ is attached to the elclouseur and an GEC is ran to the electrode from that point
Then the netural is in the single phase panle.
A sign of this would be two panels sitting side by side one three phase and one single phase. Or a wire way with the two panels sitting above it.
When we read 240 three phase it generally leads to more questions.
Just throwing out another option of why.
Old store use the three phase for compresses and such. The rest single phase.
A few pics of electrical equipment might help. Also if over head service you will have two drops for a six wire or taped at the weather head to a single four wire drop.
Also talk with your electrician and ask what he attached the netural to in the panle.
It amazing what a voltage sticker can solve.
Yeah I say 240 out of bad habit. It's 208
There's only a 3 phase breaker at the panel, in the oven are three phase breakers for the heat and circulation motor, and a 120 breaker for the controls
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
That really doesn't mean anything, but maybe no neutral? So, he connected the oven neutral to ground??? No wonder he doesn't want to say what he did. Are there any single pole breakers in that panel which would indicate a neutral is present?
-Hal
There is a new neutral run to the oven. The only way we got the oven to work was making a jumper lead from neutral to ground in the control compartment.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
But apparently the neutral bar back at the panel is not connected, I assume the new neutral was ran all the way back, it may be a panel with just mechanical equipment using three phase only, and they didn’t pull a neutral with the panel feed to save money. Hard to tell over the internet LOL!
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
You still didn't answer my question. Does the oven work now or do you still have to connect neutral to ground at the oven?
-Hal
It sounds like it's still not working. We didn't leave the wire from N to Gnd. The electrician told another tech I work with that the oven is 'feeding back to neutral'.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It sounds like the neutral/ground bond is broken or was never made in the service.
Something happened. The oven has been there for over 20 years and this came up suddenly.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
In that case, I suggest looking for the break in the neutral pathway either in the circuit or the appliance using a fall-of-potential check.
That's how we came to the idea it's a neutral issue. We ran a temporary line and neutral wire from the neutral terminal block and 120v control breaker to the digital temperature controller and it only blinked like it couldn't find stable voltage. So we took the neutral wire and touched the frame and it came on fine. That's when we reconnected everything and jumped N to line to test it and everything worked as normal.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
If you can, please send a photo of the nameplate, or at least the make/model, then we can look up it's exact requirements.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I would start at the panel and check for voltage between the ground and neutral buses, the neutral bus and the appliance circuit's neutral wire, that end of the neutral wire and the other end (might need a long piece of wire for this one), the other end and its terminal, that terminal and the next point, etc.
At some point, you should find a break in the pathway by finding voltage between two points where there should be none. You already have the ~45 volts between the neutral bus and the appliance's neutral terminal. Now you just need to narrow it down. Of course, the appliance needs to be on for this.
At some point, you should find a break in the pathway by finding voltage between two points where there should be none. You already have the ~45 volts between the neutral bus and the appliance's neutral terminal. Now you just need to narrow it down. Of course, the appliance needs to be on for this.
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