|
| Ek's Home | Forum | Chat | Electrical Links | |
| Subject - doubler breakers in panels | |
| blackrd | Cant find info in the book about doublers in a load center. youve got 42 spaces filled up, and need more capacity so you install doublers(single pole breaker with 2 tap screws or terminals). I know inspectors that ok this, but Im wondering what is the official take on this, as you are limited (by listing I beleive) to 42 circuits. Is it ok if it passes your load calc, or is it general a no-no? Im looking at the book now and dont see anything except 384-15, and according to this anything over 42 overcurrent devices is prohibited. So I assume a doubler is one overcurrent device. |
| kbsparky | I believe you are referring to what we call "piggy-back" or "tandem" circuit breakers. And no, one of those critters counts as two overcurrent devices. So, if you use them once your panel is full -- exceeding the 42 circuit limit -- you are in effect violating the Code.  In order to install any piggy-backs in a panel that exceeds the maximum allowable, you are using "non-class CTL" breakers. If you read the warning label on them, you will find that they state "For replacement use only, not for CTL assemblies" or some similar wording. A CTL assembly is "Circuit Limiting" which complies with the 42 circuit rule for any one panelboard or load center. The panels have a physical means to allow only sufficient number of breakers to meet, but not exceed that maximum. In Square D type QO load centers, it is accomplished by the use of a rather large "foot" that engages in the pan rail slot of the load center. In GE load centers, their half-size breaker uses a side-mount clip to engage the bus bar. Those bus bars are only present where the use of their half-size breaker is allowable. In most interchangeable breaker boxes (Bryant, ITE, Murray, Challenger, Homeline, etc) the bus bar is split into a "V" shape allowing the end of the breaker to penetrate the bus bar tab ½-way down. As a rule, you will find that the non-CTL breakers cost double or more what the CTL ones cost. You may also find that they out-sell the UL listed CTL breakers as well <shrug>. 
|
| blackrd | You sir are correct! In further researching I found the following,"class CTL" is the ULinc. designation for the code requirment for circuit limitation within a lighting and appliance branch circuit panelboard and means "circuit limiting"". You are to be commended for your knowledge of this aspect of NEC code. One inspector told us to use a piggyback in order to solve a capacity issue in the board. Kind of scary. |
| kbsparky | WE usually install a sub-panel when faced with a loaded to capacity panel. Especially when installing a significant amount of new loads, or new circuits into an existing structure. Although, we have "cheated" a time or 2 <sheepish grin>  Usually, however, my "cheating" consists of combining 2 circuits to a single breaker, where their connected combined loads are within a reasonable amount according to the breaker size.  Thanks for the compliments 
|
| willie | According to our local AHJ (who is quite sharp), most current breakers are listed for landing two wires under the terminal. The trick is that most panels don't have this info in them, and you almost have to call the manufacturer to find out the UL listing on this item. |
| electroman | Panels which are rated for the correct kind of tandem are going to have a dual rating such as a 20/40 or 8/16. I find this is a regular problem with homeowners who buy the 30 space panel for their new home. When I come to do the final (I know, I should count the circuits on the rough-in) they have several "for replacement use only" tandem circuit breakers landed in their service. |
| sparky13 | There are alot of good pionts here. First off tandems are scary. If you go over 42 there is trouble. A "buddy box"- sub panel is the way to go. I have only heard or seen a veeery limited amount of breakers listed for 2 wires on the terminal screw. They are not every day breakers. Alot of times a " home inspector" will write any situation like that up. Use your best judgement all. 
|
| stedder | I know QO breakers can be doubled up because of their screw-clamp design, usually the circuit directory and or information on the panel labeling lists whether or not mini breakers can be used and where they must be located as to not void any warrenties or listings. |
| Ryan_J | You can always splice in the panel as well [312.8], if that can get you anywhere. |
| blackrd | Excuse my ignorance, but when did splicing in the panel get the OK? 02 or 05? |
| Ryan_J | It has been allowed for as long as I know. In the 99' it could be found in 373-8. |
| stedder | Ryan I was taught that splicing in the panel was OK and I've never been questioned by inspectors, always passed etc. but I was working w/ an elecrtician from the city and was splicin' inside the panel and he was amazed / flabbergasted (is that still an expression) and questioned me on it but I still passed the inspection so, Huh I wonder if it's an ahj thing. |
| blackrd | I dont know where I picked it up, but I always thought it was a no-no. Perhaps it was always one of those things to avoid, and throughfolklore it became a "violation". |
| Wirenutz | the story is that the '42' was entirely arbitrary having originated from some official involved in the 1926 Waldorf Astoria fire in NYC... ergo, no rationale' so...if we have codes without rationales' do we obey them ? obviously, the argument of having some sort of benchmark exists, yet i find such rigid parameters displaying little to no thought a tad below our trade don't you? we ain't chopped liver folks, are we? or is it that we ALL would, being confronted with the prospect of circuit 43 via a 'twin' (or better cheater perhaps) sell a subpanel to our clients? just asking, you can all take off the halo's ok ? ~W~ |
| John A. Peters | quote:There was a change about five or ten years ago. That was when they drastically increased size of the panels to give much more wire bending space. If you take a look at an old FPE panel you will notice how jammed the wires are, compared to a modern panel with plenty of space around the breakers. |
| powerup | I would, without hesitation, install more than 42 breakers in a load-center. If it was rated for 42, and I was sure of the load and the condition of the load-center, and the wiring. I’m not sure, but I think the no-splice-n-panel thing went out with the narrower panels and fuse-boxes. Now it’s based on cubic inches. I still don’t like it though, old habits die hard, and it looks like someone made a mistake. |
| Ryan_J | Powerup: What about 408.15? |