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Question DetailsAsked on 11/3/2017

I have a 200 amp panel with a 50 amp breaker feeding out to two separate barns on sub panels. Is this allowed?

The two sub panels are used for lighting and outlets for water heaters for animals that pull 500-250W each. im trying to figure out what capacity each sub panel can hold amp wise since they share a 50 amp breaker. We need to add more lights and outlets to other area on the farm . Is This possible if so what do i need to do and if not what can i do?

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Specific locales have specific requirements about circuit protection, but basically you have to have 2 or sometimes 3 forms of overload protection in line in your system - in addition to GFCI or AFCI breaker requirements for certain environments. To get that subject out of the way, for a barn environment it would be safe to assume that all circuit breakers in the breaker panels should be GFCI breakers (AFCI if required by local code, but I would not use them on critical circuits like heating or chick warmers or such because they still tend to be too sensitive and trip out too easily - ditto when put on motors like well pumps).

And for my money, even if 2-wire circuits are legal, I would use 3-wire (with ground wire) wiring for safety - especially in a barn/outdoor environment - at least on any new wiring and any subsequent repairs or upgrades.

The primary circuit protection is of course the individual circuit breakers, which should be sized properly for the circuit wire size of course (factoring in length in your case because of run lengths possibly exceeding standard wire sizing assumptions - at least for the runs from house to barn or outlying poles). Each breaker should be sized for the total loads on it - a breaker cannot be larger than the wiring can safely handle, but if the loads on a circuit are light, the best protection may be a smaller breaker approximately 20% greater capacity than the anticipated circuit load. For instance, a circuit dedicated to animal heaters with say normal 10A total load on it should not have a 20A or 30A breaker even if the wiring can handle it - for a maximum rated 10A load a 15A breaker would be better protection in the event one of them starts shorting out and pulling more load. Of course, sometimes a larger breaker is needed because of motor surge loads, or say a light circuit to an outlying light pole with 3A draw from lighting might be installed with 15A or 20A wiring and breaker to accomodate a weatherproof utility outlet for power tool use at that location.

And with heater loads, to reduce the chance of a barn fire, I would suggest that each heater have its own breaker or fuse - either in the panel (separate circuit for each heater, sized to its demand), or possibly an in-line breaker or fuse for that particular heater's amperage. For instance, each 250/500W heater could have say a 5/7A in-line breaker or fuse protecting it, with several coming off one circuit which might have say a 15A breaker on it. These are available at electrical supply houses and are just "cubes" or 3' extensions cords with built-in breakers which you can put in-line at the outlet. Of course, most people do not go that far - they just count on any over-draw being because of a short, so count on the GFCI tripping out in that case. But the advantage of individual item protection is if it trips out it does not take a bunch more items out of service at the same time. This is the problem greenhouses and chicken brooding barns have - they might be able to put a lot of lights and heaters on one circuit but a single one shorting out and tripping the breaker can take out the entire operation, so it is generally better to have more circuits with each one carrying less of the critical loads.

The next source of protection is a "main breaker", which may be at the top of the panel itself (intercepting the incoming feeds before they go to the bus bars in the panel) or may be a bit further away from the panel on the feed wires leading to it. - but generally should not exceed - oh, what does the code say - something like 5 feet from the panel. This breaker is designed to prevent the entire panel from drawing unsafe amperage - either because the sum of the circuit loads is more than the panel can safely handle or in the event of a short in the panel outself. So these "main breakers" would be on the main household panel and also on on each sub-panel (which are presumably in the respective barns). This breaker (and the wiring from it feeding the panel) is normally sized for the smaller of the panel maximum rated load capacity (labelled on the panel) or the incoming power source (service drop) capacity feeding it. So, if your subpanels are 50A rated their main breakers would be not more than (and usually equal to) 50A. The actual numberical total of breakers in the panel will generally add up to more than 50A (or 50A per side if a 220/240V feed) because the "panel load" is calculated based on reasonably anticipated demands on the panel, not by assuming each circuit is loaded to full capacity at the same time. So, a 200A household panel might have 300A or more in individual breaker capacity - some all-electric houses have breakers totalling as much as twice the panel rating. The panel main breaker therefore keeps the total panel draw from being unsafe, and also protects against a failed circuit breaker failing to trip under a very high load. (Hence why holiday get-togethers and baking fests with lots of household guests trip out main breakers commonly because of most or all kitchen outlets being in use at one time along with hair dryers, clothes dryer, dishwasher, lots of lights and electronic devices, etc all in use at once when the panel demand calculation does not assume that).

The final protection is not always required, especially if the distribution./circuit breaker panel is within 5 feet of the power supply/meter panel. This would be a "household" or "master" breaker which protects the entire power supply and keeps it from pulling more than the supply wiring and service drop can provide. So, this is commonly a 100-200A range breaker (presumably 200A in your case with a 200A panel, or less if utility service drop is rated less), located within a few feet of the incoming service drop and meter - and may have more than one subpanel feeding off it.

In your case, each subpanel hopefully has both individual breakers for each circuit and a master breaker at the panel - though in a very few areas running both off one 50A master breaker may be legal. In that case, the total anticipated load (not the total of individual breaker ratings) from both panels together should not exceed 40A sustained load (sustained loads should be not more than 80% of breaker rating) in your case.

Because the two panels are protected by a 50A breaker serving as a master breaker for them, each has to be rated at least 50A capacity so if only one is drawing power at any time it cannot exceed its rated power draw without tripping that 50A breaker. Larger panel rated capacity is OK as long as it does not actually draw it - for instance, you can have a 200A panel with a 50A master breaker protecting it - just don't load it up beyond 50A calculated demand, so it would have a lot of empty slots. Of course, if both subsidiary panels are rated at 50A, if you load them up to a total of more than about 50A demand the 50A breaker will trip out.

For a farm environment, especially if heaters are critical to husbandry like chick warmers or if yard lighting is critical to security because of vandalism or theft in your area or such, you might also consider power failure alarm(s), which can be remotely alarmed into the house for instance, as a warning you have lost power at one or both the barns.

What you need to do is to tally all the circuits, what loads are them and which panel they come from, and figure the demand on each panel and breaker. You should also tally up what new loads you want to add and where - this can then be added to the demand calculation to figure which circuits can have reasonably added branches or loads added to them and whether the desired panel can handle the added load, circuit / breaker capacities, and whether the main/master breakers and supply wiring can handle the desired loads. The actual demand calculation of the expected (versus maximum rated) loads is best done by an electrician.

You may find the existing panels can handle it (either on existing or added circuits off those panels), you may need an added subpanel (which might or might not be able to come off the 200A main breaker panel if it has available slots and isnot already loaded to capacity), might have to come off the main service "before" the household panel, or might even in some cases (particularly when a lot of electric heat, non-LED yard lighting, or large electric motor or welder loads are involved) sometimes requires that your incoming service be upgraded with new larger meter panel and master breaker.

One option sometimes, when increasing incoming service capacity or when adding subpanels, is changing from one master breaker to several - tapping off individual master breakers in a "load center" near the service entry, with leads from each of those breakers going directly to individual subsidiary panels without passing through the main household distribution/breaker panel. For instance, you might (to the limit of incoming service capacity) have the 200A (or less) master breaker protecting the household panel, and individual appropriate sized breakers protecting branch leads to the barns. This can allow you (assuming service feed is appropriately sized) to have ancillary panels which pull more power than you can handle through the main household panel - again tothe limit imposed by the incoming service capacity.

It is also safer in common, and the general wiring plan for new installations like yours and for large workshop demands and any multi-phase motors or such, to run separate leads to auxiliary panels or outbuildings rather than through the household panel, to keep significant secondary panels from putting large long-term draws on the household panel. That sort of added draw through a main panel is bad practice if avoidable not only because it increases the total amperage the panel is pulling over a long term (hence increasing the chance of overheating and fire) but it also means that panel is closer to capacity so it increases the chance of accidental tripping-out of the main breaker on that panel due to an increased demand from the house due to using many appliances at one time, or a large demand coming on like power tools or such. A third factor is if everything is going through one panel, its main breaker has to be large - so it provides a much lower level of protectsion against dangerous overloading of a circuit if you have an individual circuit breaker fail to trip out in the event of an overload or short.

For a couple of examples of what an oversized main breaker can do - saw one 400A breaker panel (in a large house with oversized panel to handle large woodshop with large power tools) have a total loss fire because a short in an electric dryer (probably pulling a hundred to two hundred amps) combined with that circuit breaker fusing and failing to trip as it should have, but that large short draw was not enough to trip the 400A main breaker. If the household panel had been say a 100-150A capacity (with the woodshop load coming off a separate auxiliary panel but not as a sub-panel to the household panel) then the household panel main breaker would have probably tripped immediately and prevented the fire.

Had a similar case on my house - a patio carriage light shorted out due to faulty design (wiring got to hot because of lack of ventilation) and (startled the heck out of me as I was just coming to the door when it happened), and it arced and sprayed molten metal for about 5 feet all around as it continued to short out - but did not trip out the circuit breaker because it was on a 20A circuit with a lot of different lights on it - about half the house in total, so the short just arced like a buzz box welder but did not eceed 20A by enough to trip the breaker - went about a half minute to minute before it finally burned out the wiring and curned clear through the metal housing so stopped arcing.

An electrican can figure the allowable load capacities, the demand calculations, and determine wiring options for you - and your having the existing and planned loads (and voltage noted if 220/240v, and any multi-phase devices like large well pump or air compressor noted as well) for each circuit, demand written down neatly and identified as to panel location in advance will save a lot of his time and your money - plus give you (after finalization) with a circuit identification list. You also need to identify and label the demands as to whether they are long-term loads (like the water tank heaters if constant-on as opposed to thermostat-controlled) or short-term like maybe power tools or powered door openers or such. Lights can fall in either category - long-term for area lighting likely to stay one for many hours at a time or all night like 24 hour barn lighting or yard lighting or baby animal warming lamps, short-term for say storeroom lighting and garage door openers and the like which is turned on just for a short time to get some supplies or gain access then turned off. Most tools and on-demand water pumps and such would also fall in the short-term load category, but low-flow well pumps or irrigation pumps which run for hours at a time would be long-term loads. The one that commonly causes farm power issues is area yard sodium or halogen lighting which stay on all night and are commonly 200-500W per light.

Answered 2 years ago by LCD

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