does  not  open  immediately  when  an  overload  occurs. The bimetallic element requires a short time (length depends on the size of the overload) to respond to the heat generated by the overload current. A  magnetic  type  of  circuit  breaker  responds instantaneously  when  an  excess  of  current  flows through the breaker. A small electromagnet is used to actuate  the  breaker  mechanism.  Whenever  a predetermined  amount  of  current  flows  through  the electromagnet, enough magnetic flux is created to attract a small armature. As the armature moves, the breaker mechanism trips and opens the circuit. The thermal-magnetic circuit breaker, as the name implies, combines the features of both the thermal and the magnetic types. Of the three, the thermal-magnetic circuit breaker is preferred for general use. A small overload  actuates  the  bimetallic  strip  to  open  the  circuit on a time delay, while a large overload or short circuit actuates   the   magnetic   trip   to   open   the   circuit instantaneously. Circuit breakers are rated in amperes and volts the same as fuses and you select them on the same basis. Circuit breakers are sealed units and no attempt should be made to repair them or to adjust the ampere capacity. A defective breaker must be removed and replaced. 5-34 Circuit breakers that are to be used in circuits that may pose an added hazard to the user are made with an extra safety feature. This breaker is called a ground fault  circuit  interrupter  (GFCI).  It  is  a  thermal-magnetic breaker with an additional internal circuit that detects a current leak from the hot wire to ground and opens the breaker if that current reaches a set amount. This leakage cannot be more than 5 (±1) milliamperes (thousandths of an ampere) to ground. Most of these breakers have a test button that can be used to check the GFCI to see if it will trip when there is a fault. To install the GFCI, you connect the circuit hot wire to the breaker the same as you do on a standard breaker. The circuit neutral is connected to another terminal on the GFCI instead of to the neutral bar in the panel. The GFCI comes with an attached white neutral wire, which you then connect to the neutral bar. The NEC© requires that GFCIs be installed for several circuits used in the home.  These  circuits  include  ALL  120-volt,  single- phase, 15- and 20-ampere receptacles in bathrooms, garages, and outdoors. GFCIs may be used elsewhere when there is a need for the added protection. Now that we have discussed the various types of panelboards,  fuses,  and  circuit  breakers,  we  need  to discuss panelboard connections. Once the circuits have all been brought into the cabinet, the panelboard can be mounted in the cabinet. Also, the neutral bar and the equipment ground bar are attached to the cabinet. The ground bar must be bonded to the cabinet by either a bonding  jumper  or  the  more  common  method  of running a screw through the bar into the cabinet. The equipment ground bar and the neutral bar are not bonded together unless the panelboard also serves as the service  equipment. Quite often the panelboard is not connected until the interior wiring is done and the receptacles, switches, and  fixtures  have  been  installed.  The  method  of attaching circuit conductors is based on conductor size and  type  of  terminals  on  the  panelboard.  Small conductors, No. 10 and smaller, are normally looped around  a  screw  type  of  terminal.  Larger  conductors may  need  to  have  terminal  lugs,  attached  so  the connection can be made to screw terminals. Pressure types  of  terminals  are  often  provided  for  larger conductors,  neutral  conductors,  and  equipment- grounding   conductors. Conductors should be connected in a neat and professional manner. In many cases, conductors are connected with little excess wire. Conductors brought in through the sides of the cabinet are connected directly to the overcurrent device. Those brought in from the top or bottom of the cabinet are bent neatly opposite the fuse or circuit breaker to which they are to be attached and cut just long enough to make a good connection, as shown  in  figure  5-66.  However,  many  experienced electricians  feel  that  this  system  of  connecting conductors is not necessarily the best, even though it presents  the  most  uncluttered  look  and  leaves  more space around each conductor. These electricians usually try to leave an end on each conductor that is equal to the height plus the width of the cabinet. Each conductor is run along the panel and looped back 180 degrees before being connected to its fuse or circuit breaker. This method is shown in figure 5-67. Little added material is needed, and the extra length on the conductor permits it to be switched to another terminal on the panel if desired. Also, in the case of conductor breakage near the terminal, the conductor can be reconnected easily. The  ungrounded  conductors  in  a  fuse  panelboard are connected directly to terminals on the bus bars. In a circuit  breaker  panelboard,  the  underground  conductors are  usually  connected  to  the  circuit  breaker.  The  circuit breaker is then inserted in the panelboard. In most cases, the breaker is snapped into place and is held by spring tension. Sometimes breakers are held in the panelboard  by  a  screw.