Thread: Electrical Panel General Question

The is an older miners cabin so Im not sure the age of this panel. Zinsco breakers in the panel. Question is, what type of panel is this (split panel?). Tere is not a service disconnect breaker , this is it. Have not seen this type before.

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It is an old Sylvania Zinsco panel. Check inspectopedia.net for info on this panel.

Originally Posted by Robert Meier

Not that familiar with Zinsco but it looks like a split-bus panel which can have up to 6 service disconnects.

Agreed.

The bottom breaker of the top section is the main for the lower section.

The maximum allowed number of breakers in the top section is 6, and that includes the breaker which serves as the main for the bottom section.

Thank you

And it looks like there is a dbl tap on third breaker from the bottom

Originally Posted by Michael Moradian

And it looks like there is a dbl tap on third breaker from the bottom

Looks like two multiple taps as there are 11 conductors coming out of 8 breakers.

Also looks like there are some grounds and neutrals in the same terminal in the neutral terminal bar.

Not sure that the neutral terminal bar is intentionally bonded to ground. It may, or may not, be bonded to ground through the grounds connected to it.

Probably many more things wrong too, but the main thing wrong is that it is a Zinsco and needs to be replaced. Hopefully, the electrician doing the replacement will not make the same errors.

That is why I state "make all corrections noted in report, any additional items found during the correction work, and any non-conforming items created during the correct work". That leaves it up to the electrician to know what they are doing and then to actually do what they know.

What was the reasoning for that panel? In other words the main turned off the bottom breakers but the top few breakers had to be opened somewhere else?

Originally Posted by Gerry Bennett

What was the reasoning for that panel? In other words the main turned off the bottom breakers but the top few breakers had to be opened somewhere else?

The other 5 breakers besides the lighting main were essentially the main breaker. This was using the 6 throws of the hand rule to disconnect power.

The top half of of that MLO split bus panel has a significant number of 20A breakers, thus it may not be used as service equipment or service disconnect.

Primary for a 6-disc rule was based upon pre 05 power panel distinctions and ratings on old stab rules irrespective of load calculations presumed 10A per bus stab - utilized or not for the ratings and approvals.

IIRC limitations for all on the upper and absolute restrictions regarding the maximum rating for back fed Lighting & Appliance back fed sub-main - have no recollection of any allowing a 100 A for same - sub bus(es) limted for required protection under that.

Again the wiring diagram, label, and markings are not pictured.

Are you entirely sure Mat, that there is NOT a combination meter service ahead or other "service" equipment - even a ped or pole mount disco ahead of the cabin structure nearer the right-of-way? (or transformer bank) providing "service" to the overall property? If there was an active mine - or other facitilites this may not be "service" equipment but secondary, even older tap or feeder.

Originally Posted by Robert Meier

I see only 1-single pole 20 amp CB on the top bus with no wire connected to it. Even if there were more why would this matter?

Significant number is anything more than zero when applying your invocation or envocation of "the six" rule, as 1/6th is greater than 10% and the presence of any unmated/unmatched SP breaker in the mains bus(es) in MLO service panel equal to or less than 30A or greater than 10% 30A or less breakers manufactured to list to earlier than 05 NEC esp earlier pre-90s.

Because you referenced the "six" rule and the OP as have you, suggests or asserts propriety as "service" equipment. There is wired and present a mini non-tied 30 amp breaker (pale green). Neither permitted for this vintage equipment MLO as "service" equipment.

10% or more on the bus 30A or less = Lighting and Appliance panelboard and NOT a power panelboard. Rule of Six does and did not apply to L&ABP MLO panelboard as service equipment. Use as service equipment was and remains expressly limited as per its listed (at the time) to the standard (at the time) and its labeled and indicated restrictions and instructions which were a critical part of its listing.

Shouldn't have to connect the dots for a sparky familiar with the limitations for such vintage or type (split) panels, GTE, Sylvania, Zinsco, bryant, ge, stablok, etc.

The SP 20 A breaker's pressence on the bus(es) defeats the listed instructions and limitations for temperature, short circuit ratings, etc. for use as service equipment. Its presence and the presence of the 30A mini defeat the possibility of the use of a "six" disconnect rule for a power panelboard.

Just because the present NEC doesn't address, it does not negate the rules, definitions, and limitations of prior editions of the NEC upon which the prior editions of the listing Standards and limitations therein based upon those earlier editions of the NEC, to which this panel was tested, manufactured, and listed, were limited to.

Definitely a pretty clean panel for a Zinsco installation. It even has a separate ground bar. The reason for the split buss is money / cost. The bigger the breaker the higher the cost. With the code allowing up to six service disconnects it is cost effective in avoiding the expence associated with bigger breakers, ( disconnects ). This was particularly important in bigger commercial services where the cost of a single main breaker was painful. When manufacturing started mass producing 200 amp MCB load centers for residences like bottle caps the cost savings basically went away.

Originally Posted by Robert Meier

I see your point. I thought that the top CB was 50 amps. If it were a 50 amp as I first thought why would the mere presence of a 20 amp CB without a conductor attached change anything. Certainly it could be used to fill the blank space no?

No it (that 20A Single pole breaker - or any single pole 15 or 20A breaker of that vintage that would have been listed for use on that panel - or that panel's listed instructions would have indicated might be used upon that panel) may not be used, placed, or stabbed in that space for any purpose when that MLO panel is employed as "service equipment", its mere presence disqualifies the use of the panel as "service" equipment.

Pale green Zinsco/GTE/Sylvania is always 30 amp. The ratings would be compromised - lowest denominator - and the limititations for the equipment as service equipment as originally labeled, instructed & limited, by its original Listing and the Standard(s) of the vintage for same.

Furthermore, that replaced sub-bus(es) backfed breaker exceeds commonly employed, listed & labeled max stab rating on the primary mains bus(es) limittions for that vintge panel, whether or not it is employed as service equipment.

Once again begrudgingly schooled by H.G. Not much exposure to Zinsco, but based on H.G.'s post, I'm assuming the half sized breakers would not have been lisited / approved for use as a service disconnect. If that is correct, the O.P. panel could only accommodate three main disconnects, as it only has space for three full size two pole breakers and one of those three spaces is already in play as the split buss supply breaker. An odd panel configuration, if the no half size assumption is correct. Alternatively, if it is not a main service panel, I'm supposing it could be legally filled with half sized breakers.

Regardless of what the poster for posts 10, 12, and 15 says, that IS the service equipment - as stated by the OP (Original Poster) in the OP (Original Post).

Thus the maximum of six (6) breakers DOES apply.

There may be (are) incorrect uses within that panel, nonetheless, though, those uses DO NOT MAKE THAT *NOT* THE SERVICE EQUIPMENT for that structure (an old cabin, as described by the OP in the OP).

Installing the front brakes on the rear of a car and installing the rear brakes on the front of a car *does not change the front and rear of the car* - just means the brakes are installed incorrectly.

Garry B,

No you're missing the point completely, and added in your own invention.

When a pre-2005 manufactured panelboard (esp. a pre- mid-80s mfg split-bus) the L&APB (Lighting & Appliance PanelBoard) vs. the Power PanelBoard rules come into play.

The MLO split bus panelboards when used as service equipment did and do not permit more than 10% equal to or less than 30 amps when used as service equipment - (these must be on the sub-bus, series protected) and any panelboard with has more than 10% equal to or less than 30 amps MUST be protected ahead by no more than 2 devices) (i.e. no "six disconnect rule for L&A PanelBoards).

You'll find this still covered in your UL WhiteBook, under Panelboards, and in the appendix "marking guide" for "panelboards". This was covered in earlier editions of the NEC, and the panelboards made earlier were made to be used under their listed limitations, referencing the edition of the NEC which was in force at the TIME OF MANUFACTURE and LISTING.

single pole full size 20 amp unmated breaker may not be stabbed in the mains bus when the MLO split bus panel is employed as "service equipment" - whether or not said breaker is "feeding" or supplying anything.

That 100 amp 2p breaker likely exceeds the max permitted (as labeled/Listed at the time) max individual bus stab rating permitted for that mains bus(es) however the panel employed. Likewise the sub bus(es) are likely additionally limited to protection less than 100 amps. Most lighting & applince submains were limited to less than 80 amp protection. Of that vintage, regardless of "load calculations" each stab was "calculated" at 10 amps, actual loaded short circuit, temperature, etc. "testing" didn't take place of the vintage - listings were based on "calculations".

There are dozens of posts elsewhere on this board regarding "stab ratings" and the limitations found in earlier panels, including many readable photographs posted of the panel diagrams and limitation language, directly repeated from the vintage UL marking guide and the UL Standards for Safety applicable at the time of manufacture.

Geeze Dubaya. I got the point and do not consider mine an invention. I get the 20/1 not being acceptable in a main service application, ( BTW; is the 10% limitation based upon the supply wire size or panel rating size ? ). "any panelboard with has more than 10% equal to or less than 30 amps MUST be protected ahead by no more than 2 devices) (i.e. no "six disconnect rule for L&A PanelBoards)." This quote makes no sense to me and that point I am probably missing. Your point of the 20/1 not being legal did cause me to realize that half size breakers were probably not listed for use as main service disconnects which would be another problem w/ the panel. I do not know if their or any half sized C/Bs can be used as service disconnects - - - do you ? Repeating what I said; assuming half sized breakers are not legal as service disconnects, that panel could legally only hold three main two pole disconnects and that would make it an odd configuration for a main service application. Not illegal, just odd. Do you not agree w/ that ? I noted the 100/2 comment, but consider it speculation.

So assume the 20/1 is replaced by a blank, the 100/2 is OK and the remaining main section C/Bs are correctly wired. Could that panel possibly have been compliant with the half sized breakers ?