In the National Electric Code
is defined as the conductors and equipment that conducts electricity from the point where the electric company
's wires end and the first distribution panel
in a building
. The service defines how much energy
enters a building, which is measured by voltage
. This writeup is intended to explain to the average homeowner
the things they need to know when considering their own electrical service, and whether or not they ought to upgrade
Your electrical service begins at a thing known as your weatherhead. To spot it go outside your house and find your electric meter. Usually there will be a conduit out of the top going upward, which may extend through your roof. You will see a hemispheric part at the top that conduit which will have an opening at the bottom, from which the wires protrude. The wires will go down, and then back up, and will attach to triplex wires provided by the electric company. Your electric service begins where the wires leading to your meter splices to the wires provided by the electric company. If your service is fed underground then a pipe will come up into your meter from below and a weatherhead will probably be found at a nearby utility pole or a transformer located on the ground. Usually the wires will be direct buried, which means there is no pipe protecting them. Dig nearby only with care, though you should have a minimum of 18" and some sand around the cable to give you warning.
Triplex is three aluminum conductors wrapped around a steel cable. it extends from the utility pole overhead to your house, and the steel cable is there to bear the weight. There will be porcelain eye attached to your house (or rising conduit, if it is thick enough) that the steel piece will be attached to using a wedge clamp.
The wires will go downward and then back up to the weatherhead, forming a drip loop. A drip loop is exactly what it sounds like, the loop gives rainwater a place to drip off so it isn't carried by convection up and into the pipe, and then down the pipe into your electrical system.
The pipe and the weatherhead coming out of your meter is called a service riser. Alternately, the conductors can be run underground from the utility pole to your meter. You pay for those conductors, so the riser is at the pole. Underground services cost more, but look better.
Next in the chain is your electric meter, which operates by induction. After the meter the wires will move via some type of raceway to the first means of disconnect.
All services must have a first means of disconnect, a place where all power to the premises can be shut off, which makes the building safer to work on. In the NEC. The NEC allows for up to six switches at the first means of disconnect. This means that one riser can be broken up for individual apartments, or something tiny like a kiosk might simply have a small six space panel, and slide beside the whole disconnect rule. There are some older panels known as split bus where there is a main breaker for the 120 volt circuits where a limited number of 220 volt circuits are, in effect, their own disconnects. Those panels are not legal for new or replacement installations today.
The disconnect must be located where the service enters the building, or within three feet of where the service enters the building. If your house is built on a concrete slab and the service comes up from underground, it is said to enter the building the moment it exits the concrete. If the wires are run through a basement or crawl space it enters the building whereever the service penetrates the siding.
So, if your panelboard is located on an outside wall and the service enters right there then you can use the main breaker of your panel as the first means of disconnect. If it has to travel a way, as in my house, you have to put the disconnect outside the building. Most homeowners get a weather rated NEMA box, which has a large circuit breaker in it. I put a fused disconnect on my house, mostly because they look cooler.
Your first means of disconnect defines your service. The wires and panelboard must be rated to comfortably the power the disconnect will pass. In the US the minumum new residential service is 100 amperes at 240 volts. Raise that to 200 amperes if your home has electric heat, and there are other calculations based on expected branch circuit and lighting loads that may raise the minimum service over 100 amps, but 100 will do for most people. In fact, that's what i put in my house, which is small, and has gas everything.
Many people want to have their electrical service upgraded to get 220. Folks, if you live in the US or Canada, and you're not the unabomber you already have "220".
Residential service in the United States and Canada bring is two conductors, each rated at between 110 and 120 volts AC. They are the same phase, which means that the voltage waves on both peak at the same instant. The two conductors can be combined to make between 220 and 240 AC volts. The voltage you get is not defined by your electrician but by the power company. The only way you could not have '220' is if you have lost one of those conductors, or if the utility transformer is bad. In either case, the issue is one of repair and not upgrade.
When you upgrade your service, you increase the level of current coming into the bulding, as measured in amps. Amps and voltage confuse many people so they are explained briefly here. Ohm's Law shows that voltage and amperage are two sides of the same coin. Transformers convert volts to amps and vice-versa. What you need to understand is the diference. Voltage is sort of analogous to pressure, current to quantity. When you squeeze your finger over the end of a hose you are doing something like increasing the voltage coming out of the hose, The total amout of water does not change. Only the pressure does, and with it the distance from which you can squirt someone. The insulation on wire is matched to voltage, but fortunately for us all wire approved in homes and businesses is approved for any voltage which might be supplied. Only in industrial applications would wire with a higher voltage rating be required.
Current is measured in amps, and since you already have '220' what you're really doing when you upgrade your service is bringing more of those amp things in. That requires larger wire-- more copper or aluminum. The upshot of this is that when you upgrade your service, the conductors running from your panelboard, your panelboard itself, and the raceways itself will have to be upsized to accomodate the increased amperage. This is what creates much of the cost involved in upgrading your service.
Your panelboard must be rated for the amperage coming into the building. And it must also have sufficient breaker spaces to serve all the circuits coming into the building. Larger panels generally may accommodate more circuit breakers. Most people change their panel more to get more breaker spaces then additional current capacity. Either is a valid reason for a service upgrade.
What upgrading your service can do is bring more power into the house, which allows you to run more gizmos. Theoretically. But the amont of power in your bathroom is defined by the number of and size of wires coming into your bathroom.
For example, assume you have a problem with your hair dryer taking out the kitchen and bedroom every time you use it. The amount of power going to your hair dryer is limited by the size of wire going over to the receptacle the styling appliance is plugged into. If the conductors are 14 AWG copper, they are rated by the NEC in table 310-16 for 15 amperes in a branch circuit. Any more current and the 14 AWG wire will heat up because resistance is a property of surface area (of the wire) and current flowing. Over 15 amps and the resistance grows high enough to make the wire act like a heating element. This is why the code specifies the maximum overcurrent protection permitted for any given wire size. When the wires in your wall are a number 14 and I change your panel, i will hook those up to a 15 amp curcuit breaker even if you hair dryer keeps tripping breakers. Better you reset the breaker than replace your house. Unless there was a problem with an older breaker, changing to a new panel has NOT allieviated your local power problem. To make the dryer problem go away you will have to run a new circuit to ensure the dryer isn't plugged in with the microwave any more. OR you may choose to run larger wires so the breaker size can be upgraded. I would almost always recommend simply adding the additional circuit.
Changing your service will not get rid of the knob and tube. Many homes built in the early 20th century are wired using a means called 'knob and tube". The style gets its name because the wires are wound around porcelain 'knobs' where it changes direction. Where the wire passes through a stud or some other structural member, it passes through a porcelain 'tube' which insulates the wire.
Knob and tube wiring is not inherently unsafe. Porcelain is a wonderful insulator, the same stuff used used in the towers used to conduct power cross country, at voltages that can exceed 600Kv. The wire can be bare, and as long as the knobs and tubes are in shape, there will be no short.
That doesn't mean it's good. Electricity only works in a circuit. In a modern circuit power passes through an overcurrent protection device (fuse or circuit breaker] goes out to an appliance (say a lamp) and then returns to ground. The out leg is called the 'hot' and the return the neutral. Without both legs no circuit will operate. In a modern building both wires by code are run together, and identified by color. Neutrals are by code white or gray, while hots can be any other color except green which is used for equipment chassis grounding. If you measure voltage on an 120v circuit the hot will measure about 120v and the neutral will measure either zero (if the circuit is not being used at the moment) or something less, say 30-40v. In a simple knob and tube circuit one wire leaves the panel, passes through a switch, then runs up across the celing to the light and from there back to the neutral bus of the panel. Those circuits can split at any point, and again, one wire returns.
That's fine as long as nothing gets added or changed. But neither Thomas Edison or Nikola Tesla thought people would be using home computer networks and microwave ovens, dishwashers, air conditioning and a zillion other things we take for granted, but must be retrofitted in older homes. The truth is we use a lot more power than we used to.
So if you want me to add a couple outlets to your office, I can do that. But if I try to get my circuit from the nearest knob and tube box, which wire is my neutral? Is it really a neutral, or a switch leg? If the wire is a neutral the voltage might be something like 30, but without a defined ground my voltage tester often won't read properly. Simply put, working on an old knob and tube system involves flying blind. Often it is better to simply replace the wires. Today the NEC requires the neutrals and ungrounded conductors ('hot') be run together, and the neutral be identified by color--namely white. If a newer home (post 1950) needs a new outlet, often i can get power from nearby and be sure what's what.
A service change won't get rid of the knob and tube, or keep your hair dryer from blowing breakers. You need to run new branch circuit wiring for that. Running new branch circuits is expensive once the walls have been covered because it takes a lot of work to get the wires where they are needed. Often it means replacing chunks of the wall and celling.
Getting rid of your fuses is also not the advantage many people think it is (see Fuses versus Circuit Breakers). Fuses are dead nuts reliable at any age. But the old type 'H' screw in fuses used in very old homes are all one size. if your hair dryer blows, many people in such homes simply pull out the 20 amp fuse and replace it with the 30. They often get away with it, because the NEC is all about overbuilding. Sadly, upsizing is easy. If a 30 amp fuse is all you have left and you just blew a fifteen, many people will just install the thirty anyway. Fires start that way.
But breakers do wear out, and some older breakers-- notably Federal Pacific Electric are nothing but junk. Upgrading an old panel of questionable quality often does make you safer.
On the other hand, you may wish to change your service anyway. We do use many appliances that did not exist when I was born. Today the NEC requires two separate 20 amp services to every kitchen and dining area, as a minimum, with a number of other dedicated circuit as well. The simple fact is we use more power, and if your service riser gets warm when you have the AC cranking, it might be time for an upgrade. And if you want to buld a shop, put in mondo christmas lights or enlarge your home a service upgrade my be essential.
Electrical services are the first part of your home electrical system. They define how much power you have, and what you can ultimately do on your property But they don't affect the power going into your bedroom. If you are considering an upgrade, think first about what you want to do with the power. I carry an amprobe with me, a device where i can measure the current being used in real time. Many times service changes are unnecessary, and bring more style points than real utility. Understand what your problem is before you call your electrician will make it easier for him to decide what is needed.