Tandem Breakers.

J

John165

Member
Location
New Mexico
Occupation
Journeyman
I have been told that you can not use a tandem breaker on an old ungrounded 2 wire system, even if they panel is rated for them. I tried looking in art 240 & others, can't find anything about it. I don't see why you could not, does any body know about this. Thanks John
 
John165 said:
I have been told that you can not use a tandem breaker on an old ungrounded 2 wire system, even if they panel is rated for them. I tried looking in art 240 & others, can't find anything about it. I don't see why you could not, does any body know about this. Thanks John
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I don't think there is any code rule that would prohibit that.
 
Perhaps terminology is part of any confusion here?

Ungrounded system is not the same thing as a having wiring methods with no equipment grounding conductor.

Old homes with no equipment grounding conductors run with branch circuits still were normally supplied with a grounded conductor or at least were upgraded to a supply with a grounded conductor at some point.

Old K&T installs where you often see a fuse in both circuit conductors possibly did not have a grounded conductor when they were first installed.

Old farmhouses sometimes had wiring installed before there was any utility power and they ran mostly just some lights off batteries and wind driven generators. They often ran the same wiring methods as if it were utility supplied as they were anticipating it would eventually get connected to a utility supply.

Still a tandem breaker is nothing more than two overcurrent devices in the same frame, presence or non presence of a grounded conductor will not effect operation of the individual overcurrent devices they respond to currents higher than the trip setting either way.
 
electrofelon said:
I heard a good one on tandem breakers a few months ago: an inspector told me you can only use tandems if you "need" the extra spaces. 🤣
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Good to know. Surely you ask for a code reference while holding back 🤣.

I'll Google to see what it says.

Sure enough
 

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infinity said:
Electrical related AI answers are still terrible.
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AI content from general sources such as Google, Facebook, etc. for most anything is terrible.

If say Mike Holt had AI on his site at least it would be more geared toward specific content and have more of a chance of being something you can trust to some extent.

But IMO AI doesn't exist, they just have some things out there that sort of mimic what real AI would be like. Real AI would have the ability to think on it's own. What we have still only follows what it is programmed to do. Some things just have a wider variety of what they can analyze compared to others, they still can not respond with something totally out of the blue, the response will still be something based on what it was programmed to do.
 
Many modern panels are listed for all tandem breakers. I have an Eaton 40/80 which allows tandems in every slot.
 
Tulsa Electrician said:
Good to know. Surely you ask for a code reference while holding back 🤣.

I'll Google to see what it says.

Sure enough
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That answer likely was found by the AI in some forum and was only an opinion of whoever wrote it. Note that that response did not much for facts or references to support the answer
 
kwired said:
But IMO AI doesn't exist, they just have some things out there that sort of mimic what real AI would be like.
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So, you're saying that we only have artificial artificial intelligence, not genuine artificial intelligence? :unsure:
 
electrofelon said:
I heard a good one on tandem breakers a few months ago: an inspector told me you can only use tandems if you "need" the extra spaces. 🤣
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Prior to AFCI's was not unheard of to see new builds with the panel full of twin breakers, never liked that but there is a difference between opinion, & facts.
 
John165 said:
I have been told that you can not use a tandem breaker on an old ungrounded 2 wire system, even if they panel is rated for them. I tried looking in art 240 & others, can't find anything about it. I don't see why you could not, does any body know about this. Thanks John
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The issue is slash-rated vs straight rated breakers.

A slash rating, such as 120/240V, means it's rated for 240V between any pair of conductors in the system, and not more than 120V to ground on the particular circuit where it's used. What you need for using on an ungrounded system, are straight-rated breakers, that are rated for the full 240V, regardless of where ground is within that range. An ungrounded system may generally be in a metastable state of being 120V to ground, but there's no guarantee that it remains that way. It could have a single line-to-ground fault, that goes undetected.

The majority of 1-pole breakers in general, are slash-rated. This is likely the case for tandem breakers as well.
 
kwired said:
AI content from general sources such as Google, Facebook, etc. for most anything is terrible.

If say Mike Holt had AI on his site at least it would be more geared toward specific content and have more of a chance of being something you can trust to some extent.

But IMO AI doesn't exist, they just have some things out there that sort of mimic what real AI would be like. Real AI would have the ability to think on it's own. What we have still only follows what it is programmed to do. Some things just have a wider variety of what they can analyze compared to others, they still can not respond with something totally out of the blue, the response will still be something based on what it was programmed to do.
Click to expand...
It’s just a super fast search engine branded as AI. Garbage in, garbage out!
 
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