Do I Size For 120 Or 240 Volt Service

Electric Service Capacity

Determining the Chapters of a Residential Electric Service

This commodity will provide an agreement of how to decide the chapters of a residential electricservice.  Quite oftentimes nosotros are asked the seemingly simple question "What is the size of my electric service"?  In most cases this is a simple question to answer, as long every bit one knows what to look for.

Volts vs. Amperes Showtime, information technology is important to empathize that the capacity of an electric service is measured in amperage or current, not in volts.  Amperage is the period charge per unit of the electric electric current that is available.  A home with 150 amp service can operate more electric appliances than one with 100 amps.  Our reliance on freezers, kitchen appliances with clocks, timers and artificial intelligence, charging stations for cell phones/PDA's, large TV's, stereos, fans, dishwashers and a host of other consumption devices take all merely rendered a 100 amp service obsolete.  Now we are commencement to charge our automobiles!  A 200 amp service is the new normal in new structure. Residential electrical services enter buildings in two forms, 120 volts and 240 volts.  These are nominal numbers, which ways that the actual voltage in the house can vary.  Ofttimes times, 240 volt electric service is referred to as "220".  Nigh all houses have both 120 volt service and 240 volt service (these can as well be referred to as 110 volt and 220 volt).  110 voltage tin exist used interchangeable with 120 volts, and 220 voltage is interchangeable with 240 volts. To help understand the deviation between volts and amperes, the electric service can be compared to the flow of water in a piping.  The corporeality of h2o flowing in a pipe is typically measured in a volume of water per unit mensurate of time.  As an example, 10 gallons per minute of water may catamenia through a certain pipe.  This period rate of water is analogous to amperage or current in an electric wire.  Current is the measurement of the amount of electric service that is "flowing" through the wire.  The pressure level of the water flowing through the pipe is not a measurement of the amount of water, only rather the amount of free energy of the water inside the pipe.  Similarly the voltage carried past an electric wire is a measurement of the amount, or blazon, of energy that is being carried. The amperage of an electric service is the capacity of the service, and the voltage of the service (120 volts or 240 volts) is a determination of the blazon of electricity that is available.  In residential applications 120 volt service is utilized for lights, outlets, small appliances (such as microwave ovens, irons, toasters, clocks, televisions) etc.  "220" volt service is utilized for larger electrical appliances such as air conditioning units, electric dryers, electric ranges, some electrical heaters, etc.  Virtually all modern homes will have 220 volt electric service into the house.  In that location are still a few houses around that practise non have 220 volt adequacy at the nowadays fourth dimension.  These are unremarkably old homes that take non had electrical upgrades for a period of many years.  These are rare. An easy way of determining whether a firm has 220 volt or only 120 volt electrical service would be to await at the overhead electric wire where it connects to the firm (if it's an underground service, information technology almost certainly has 220 volt capacity).  The overhead wire is referred to as the service drib or service lateral.  At that place are three wires. Two of the wires are "hot legs", and there is a separate neutral wire.  The neutral is usually bare metal, significant that yous tin actually see the metallic wire.  The hot legs are insulated, typically with a black rubber covering. This overhead wire is connected to the electric service cable, or "riser" for the house at the point where the overhead wire is attached to the building.  If all three wires are continued to the service "riser" that runs down the wall of the house, you tin can conclude that there is both 110 volt and 220 volt service for the business firm.  This is because each of the "hot legs" carries 120 volts, together providing 240 volt or "220", to the house.  To the contrary, if one of the hot wires for the overhead service is not connected to the riser cable on the house (just instead is just tied back loosely) then the firm is only provided with 120 volt service.  Again, this would be rare.  Usually these houses but have thirty ampere capacity for the electric service, and the electrical panel is a very quondam fuse panel.  It is important to note that even about fuse panels that remain in utilise today do have 220 volt service.

This photo shows an overhead service with 240 volt capability. Notation that both "hot" wires are attached. If one of them were not continued, the house would merely have 120 volt service.

Determining the Chapters of the Service: The electrical service capacities that one might meet in residential buildings are 30 amperes, 60 amperes, 100 amperes, 125 amperes, 150 amperes, and 200 amperes.  In a few instances the capacity is greater than 200 amperes, but this would merely exist the instance for large modern upscale homes with greater electrical needs.  We offer the following in regard to these various capacities:

• 30 Ampere.  As discussed above, 30 ampere service has become quite a rarity.  A xxx ampere service would only be of 120 volt capability.  Those rare cases where 30 ampere service is found would be small-scale older homes that have been lived in by the same family unit or person  for a very long time, and the need for modernization or upgrade has not presented  itself.  This service is considered inadequate and dangerous for modern living.
• 60 Ampere.   This is typically the lowest chapters for a 120/240 volt service, but it is sometimes but 120 volt.  This capacity is considered to exist marginal at all-time for modern living.  Quite often, threescore ampere service too includes the presence of an old fuse panel, every bit opposed to the more modern excursion billow panel.
• 100 Ampere.   A big number of existing average size homes has 100 ampere capacity electric services.  Boilerplate size homes with gas or oil heating systems and hot water systems generally practice not need an electric service greater than 100 amperes chapters.  Of course, this can also depend on the electrical usage of the occupants, and the utilize of other electrical appliances.
• 125 Amperes. These are non as common and will be discussed at the finish of this document.
• 150 Amperes. Common practise is such that this has get the typical minimum that might be installed in modern construction for a single family home or for an upgrade in an  existing home.
• 200 Amperes. This is becoming the norm for modern single family residential structure and upgrades.  In many instances it is not a necessity, but it is installed routinely in new construction.

What is the Chapters? The chapters of the electric service in a house is determined by the lowest capacity of iii components: the capacity of the service entry cablevision (the riser cable feeding the business firm), the capacity of the primary electric panel, and the capacity of the primary disconnect.  In almost cases these 3 factors are the same.  In other words, it is very mutual for a 100 ampere capacity riser cablevision to feed a 100 ampere chapters circuit breaker panel with a 100 ampere capacity primary disconnect. Capacity of the Service Entry Usher

Sometimes the bodily capacity of the service entry cable is printed directly on the cable.  Unfortunately this is non common, simply when looking at some cables you volition see "100A" or "150A".  This hands identifies the capacity of the cable.  More often, the chapters of the cablevision tin exist estimated past the size of the cable:

– 60 ampere chapters cables are betwixt 3/4 and 7/8 inch wide.

– 100 ampere capacity cables are approximately ane inch wide.

– 150 ampere chapters cables are approximately i-one/4 inches wide.

– 200 ampere capacity cables are typically 1 and ane/2 inch broad.

The width of the cable can vary depending on whether it is a copper (older) or aluminum cable, and also depending on the material of the outer jacketing.

   This cable is labeled as 100 ampere

While this 100 amp cablevision is 1" wide

150 amp cablevision

200 amp cablevision

Panel Rating The rating of a panel is normally indicated on the label within of the panel door.  Sometimes the label is inside the panel, and you would take to take the panel cover off to gain admission.  This is not recommended unless you are very familiar with working with electricity and opening electrical panels.  These labels will typically bespeak "200 amp max. capacity" or "100A maximum chapters".

The label in this panel indicates 200 ampere max chapters

Capacity of Primary Disconnect Nearly modern panels take a single chief disconnect.  Often times, this disconnect is labeled as the "primary".  The capacity of the unit is labeled on the disconnect.  Information technology will typically indicate "100A", "150A", or "200A".  This is not true with split passenger vehicle panels and older fuse boxes (this will be discussed below).

150 amp main

100 amp main

As you tin can see from the to a higher place, if y'all were to see that a panel is rated at 150 amperes maximum, and information technology is equipped with a 150 ampere primary disconnect, and it is fed by a 150 ampere cable, you tin conclude that the service is 150 amperes capacity. There are instances when the 3 determining factors are not equal.  For case, if a 100 ampere capacity cable is feeding a 150 ampere capacity panel with a 150 ampere chapters disconnect, the service would be considered a 100 ampere capacity service.  The cable would be the limiting factor.  In addition, this would be an unsafe condition since the cable would non be of big enough chapters to withstand the potential for 150 amperes of current that would be permitted by the panel and disconnect.  The cable would be considered as undersized and replacement with an appropriately sized cablevision would exist recommended for rubber reasons.  On the other hand, a 150 ampere cable feeding a 100 ampere chapters console and disconnect would be considered a 100 ampere capacity service and it would also be considered safe (the cable can be oversized but it cannot be undersized). Multi-family unit Buildings Information technology is often times the case that multi-family residences accept split up or individual electrical services for each apartment.  In these cases it is common for a single big service entry cable to feed a number of electric meters.  Each individual meter so feeds each individual electrical panel.  The capacity of the service for each apartment is determined by the lowest capacity of the cable feeding each of the individual panels, the rating of the individual panels, and the disconnect.  It is non uncommon for individual apartments to have a service chapters of sixty, seventy, or 100 amperes.

Electric service for a 2 family unit house

Split up Osculation Panels Defoliation sometimes arises when the utilise of split up buss panels comes into play.  These types of panels were utilized with great frequency effectually the 1950'south and 60's.  They are non equipped with a single disconnect, although there is usually a circuit billow labeled as a "master".  The electric service connection into a carve up double-decker console volition simultaneously provide ability to two, three, four, five, or six disconnects (fuses or breakers).  The fuse or circuit billow that is labeled as "main" simply controls the power to some of the other circuits.    For a split osculation panel the size or chapters of the service is adamant by the size of the cable and the rating of the panel (since there is no single main disconnect).  It is very common for split kiss panels to accept a rating of 125 ampere maximum capacity.  Information technology is also mutual for these panels to be fed with a 100 capacity cable.  This service would be considered of 100 amperes chapters (every bit dictated past the cable).  125 ampere capacity services are rare due to the fact that 125 ampere capacity service entry cables are a rarity. Electrical codes for existing services do not require that a panel be equipped with a single main disconnect.  This is why split buss panels remain in utilise today.  They are not utilized for new installations, but many of the panels are still in employ.  Electric standards practice limit the number of main disconnects to six.  This is commonly referred to as the "6 throw rule".  What it ways that one must exist able to plow off all the electrical service to the house with no more than half dozen main disconnects.

This is a split up bus console.  The upper section has the disconnect. The disconnect that is labeled "M" shuts off the lower section of breakers. Those labeled ii thru 9 are individual disconnects. This console violates the six throw rule.

The Building Inspector

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