200 Amp Panel with 150 Amp Main Breaker?

10 replies [Last post]
sms88's picture
Joined: 2015-04-10

There's an installation where the feed is only suitable for a 150 amp panel to replace a Zinsco 100 amp panel, but the only panel that will fit is a 200 amp combination load center.

The neighboring property used a 200 amp panel but used a 150 amp main breaker instead of the 200 amp breaker. They used a Square D SC816D200C. It passed inspection.

Is it acceptable to downsize the main breaker like that? The buss is still 200 amps and someone could, in the future, put in a 200 amp main breaker thinking that it was okay because it's a 200 amp panel.

Sparky43207's picture
Joined: 2015-04-03

I don't see any problem with this. The main breaker is there to protect the bus from an over current condition.

powertech1970's picture
Joined: 2015-03-19

The same could be said about any circuit in a panel. For instance, someone could replace a 2 pole 20 amp breaker with a 2 pole 50 amp on a hot water heater at some point in the future.

It is impossible to prevent someone from improperly altering an electrical system no matter what the case may be.

Alan G.'s picture
Joined: 2015-08-29

This is okay to do, you cannot control what an unlicensed person may do in the future.

IEC's picture
Joined: 2015-09-24

Downsizing the OCPD is perfectly acceptable providing that your installation meets the following:

Dwelling calculations do not exceed 150A
SEC is sized for 150A or larger (tap extension applies)

Using the "next size up" rule, you will need the SEC sized at #1 CU or 2/0 AL minimum for a 150A OCPD (assuming no tap rule is used).

If you have this, you are good to go.

techtonix's picture
Joined: 2017-03-25

I have a very similar issue but FAILED inspection from the electric utility while PASSING inspection from the City, so obviously there is a disagreement on this load center.

I am writing a bad review because of how this Load Center didn't pass through Inspection with my local electric utility due to the manufacturer's inconsistency in marking and labeling. Let me explain.

This 150A load center shares the same body as the 200A model. On the body itself the load center is listed at 200A, however, the permanently installed main breaker is rated at 150A as the serial number and description also agree with. Because the main breaker and serial number say 150A, and because this is what I pulled a permit for, I sized the overhead conduit and wiring to 1.5 in. diameter, which is appropriate as per their specs. The electric utility inspector saw the 200A rating on the body of the box and failed the inspection stating that the conduit should be 2 in. diameter. This would require me to buy entirely new hardware and copper wiring throughout, and re-do everything -- costing me easily $300 and setting construction back two weeks. All of these problems because of a typo or economized factory specs.

What do you all think?

100 td's picture
Joined: 2017-04-20

I am from Australia, but the basics should be the same.

You may buy a 100A, 32-pole load center because you have lots of small individual circuits you need to keep separately isolated. But you actually need 42 poles, so you install a 200A load center. However, your maximum demand (total load or whatever you call it) and service size required is a total of 100A. You fit a 100A breaker and size conduits, etc. to the requirements/regulations of the service that you require, which is 100A, and you order a 100A service to feed the board.

It's like running a long distance with a large cable to reduce voltage drop, you size the circuit breaker for the protection level you require, not on the physical cable size. (You can go smaller with protection, but not bigger than the cable spec.). If you have a look at a lot of load centers the bus bar is probably the same thickness for different cenrres, only the C/B changes. (Though with cost cutting these days what used to be the same may now be slightly smaller to save costs).

Just because your load center bus bar can carry a maximum of 200A, doesn't mean it has to. It's like installing a 50A isolator/switch on a 15A circuit. (Note I said isolator) The isolator has the ability to isolate a 50A circuit, it only has 15A on it. All good.

Depending upon your regulations you may need to remark it or identify that the maximum breaker and service size is 150A, but using more capable equipment should not be a problem, and changing it out would be ludicrous, someone needs their head examined. If you can find anywhere in your regulations that say using a bigger conductor or bus system than the required current to flow through it is banned, you guys have serious problems. However, you may have some technical jargon in the regs regarding the marking of boards and circuit breakers?

Hope it works out.

dcarmine's picture
Joined: 2015-02-02

I think that the utility inspector is wrong in this case. I would check into what your options are for appealing this decision.

user-1207832's picture
Joined: 2017-04-21

Yes, but call the inspector and ask first. It might be a good idea to call the power company's engineer and tell him your plan too. If the service lateral or even the transformer is too small, a little communication could alleviate future problems.

Never assume and maintain good relations with everyone. It's one of your most important tools. Peace and good luck!

user-1207832's picture
Joined: 2017-04-21

The short answer is yes. The NEC rule of thumb is: Conductor rating can be a higher amperage rating (larger sized wire than the overcurrent protection ampere rating**); and overcurrent protection can be a lower ampere rating (rated for a smaller sized wire). But here are 2 things to know:
1) Many NEC inspectors and jurisdictions will have subtle differences from NEC requirements. Remember, the NEC is the minimum requirement for electrical installation. So, in certain situations they may require a little more. For example: No more than 3 outlets on a kitchen small appliance circuit or when extending an existing circuit, not allowing an increase in conductor size.
2) Every electric utility company (that I've worked with) will have a spec book or at least spec sheets showing their requirements for equipment and installations. Such as, requirements for temporaries, UG service laterals, OH service drops, consumer provided property poles, etc. Some of the service provider's (utility.company's) specs won't necessarily and most likely don't match with every NEC and or local inspector's/ jurisdiction's requirements.

So, this is not only an electrician lesson, but a very valuable life lesson. Communication is arguably the best tool in your pouch. Sometimes, we all learn answers after, to the questions we should have asked before.

When estimating or if T&M, before starting a job (especially in a new area), I always establish a relationship with the electrical inspector and Utility Company's engineer. Now, you will too.

What to do now. Do you want to be happy or do you want to be right? You say both? Well you can't! If you want to be right, then make a big stink, anger the ones that you will be constantly running into during your career and get a reputation as a hot head. If you want to be happy, go to the power company's engineering department, ask for a spec book, find the sheet that addresses your situation, and see what the inspector referenced to fail your installation.Then, ask if you might be able to speak with the chief engineer. Explain your situation. Unless this inspector is green (and that might be the problem), then this has happened before. Ask if there is any latitude or acceptable solution (other than replacing the W/H, conduit, hub, straps, etc.). For example: Attaching a permanent non- removable label on the cover (MAX*150 AMP*MAX). I would also speak with the building departments administrator, about including a spec sheet or at least a courtesy reminder about the utility company's requirements when issuing their permits.

Here is your chance to help solve a problem or cause one. Your Integrity is more valuable than all the tools in your pouch. Peace and hang tough, French.

** Remember the grounding conductor increases, too.

CodeQuandary's picture
Joined: 2014-07-27

To my mind, there's absolutely no problem with a smaller breaker applied to a larger wire/busbar. In fact, there's at least one case in which you might do this purposely.

For generators or solar PV or other Interconnected Electric Power Production Systems, Sec. 705.12(D)(2) states "the sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed 120% of the rating of the busbar or conductor". So for example, if there is a 200A panel with a 200A main, one can install 40A worth of backfed breakers. HOWEVER: if you have an oversized panel (busbar, really) wrt the main, you can do better: a 200A panel with a 150A main breaker will give you 90A of backfed capacity.

In fact, in the case of a "green" house with very efficient appliances/equipment and lighting, and the desire to achieve "net zero" (i.e., install a fairly large PV system), one might downgrade the main (if compatible equipment is available and no other issues apply) in order to increase backfed capacity. In no case can you backfeed more than the main as per Sec. 705.12(A).

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