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# Why relay contact haS two different ratings for AC VOLTAGE and DC VOLTAGE?

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###### 2011-02-03 18:15:48
AnswerRelays rated for AC/DC use: the DC rating being lower than the AC, This is because DC can establish an arc across the contacts which cause the contacts to burn more,so they are rated lower.When I use relays on DC I will use double pole relays an put the contacts in series this gives a wider gap when the relay opens and helps exstinguish the arc quicker.Hope this helps.

AC IS +/- WHILE DC IS JUST A LEVEL AC120 MUST WITHSTAND THE PEAK VOLTAGE

Reply: How is putting the two sets contacts in series going to help?The same potential is still being broken at the first set of contacts.>-------------0___0--------0___0---------->Parallel would make more sense to me, since then the current would be split between the two sets of contacts.

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## Related Questions

Overload can cause contact chatter. Once the contact closes, the voltage in the circuit collapses and that causes the relay to drop out. At this pint the relay energizes, since the voltage is back. This cycle will continue on.

Generally speaking, a relay is an electrically operated switch. As such, there are two sets of ratings associated with a relay. The operating voltage will be specified, and the ratings of the contacts are also set down. As regards exceeding the operating voltage, this will cause excessive current to flow in the relay when it is energized. If the voltage is not significantly higher than the rating, and if the relay is not operated often or for long, it will function normally, but probably with a shorter life. At some point, excessive operating voltage will cause the coil in the relay to fail. Operating a relay to energize an electrical circuit with a higher voltage or current than the relay is designed for will shorten the life of the contacts in the relay. Higher voltage and current will quickly burn the contacts and destroy them. This is particularly true if that voltage or current is significantly higher than the ratings set by those who designed and constructed the relay. Things might work for a short time, but not for long.

On the side of the relay there is a name plate that tells you the current carrying capacity of the contacts. It gives you the ratings at different AC voltages and a DC rating of the contacts at different voltages.

if you have checked the voltage with a dvom then you need to verify that the power source at the fuel pump relay is correct, if it has the correct voltage pre-relay then your problem is post-relay. if the voltage is not correct pre-relay then simply trace and repair the power source. if the problem is post relay then check the output voltage directly at the relay, if voltage is good trace and repair line from relay to pump. if voltage is not correct then replace the fuel pump relay

The fact that it is a dry contact has nothing to do with the amount of voltage it will handle. Contact voltage capacities are rated by the air space between live parts. The further the space, the higher the voltage will be allowed. What limits the contacts are the amount of current they can conduct. Usually relay contacts have the contact rating printed on the side of the relay enclosure. The terminology of a dry contact is, a contact in another piece of equipment that is used to close a relay in a "hot" complete circuit. e.g. An automatic transfer switch has a dry contact that when it closes on a power failure it closes the circuit for the engine start circuit to start the generator.

Typically, when the coil voltage on a relay is decreased gradually, the relay "hold" will release at a certain voltage. This is usually defined as the Drop-out voltage (defined at some minimum value). Now, in the case of latching relay, the Drop-out voltage is called the Reset voltage.

The current ratings of the contacts of a relay are written on the side of the protective envelope that covers the contacts.

a relay that operates wen the voltage exceeds a particular set value is called over voltage relay

Under voltage relay provides a signal (Contacts) when the supplied voltage drops below a preset value.

The exact measurement of voltage from ECU to fuel pump relay 94 Hyundai Scoupe is unknown. Test it on your neighbour first. If he passes out upon contact, then it is good to go.

The contact rating is normally given in AMPs or HP and refers to the load the "switch" in the relay can handle. The manufacture will specify the relay contact rating in the data sheet. This rating depends on the current being controlled by the relay, the connection type (how the relay is mounted) and the duty. A Normally open relay in pilot duty (clicked closed all day) may be only 10% of the same relay in intermitted contact duty. DC current requires a higher contact rating then AC. For example a relay rated at 1A @ 24vdc should also handle 1A @ 120vac and as the voltage increases the contact rating will lessen.

The voltage for a potential relay will depend on the circuit that the relay is installed in. The relay can be made for low voltages (5v) to higher voltages (440.)

0v The relay is designed to act as a switch when voltage is applied across the coil. The contacts open or close but only pass through whatever is connected to those terminals. &lt;&lt;&gt;&gt; When a relay coil is energized the relay's contact change status. The closed set of contacts will open. The 120 volt circuit that is connected will turn off. As to the voltage at the contact terminals, it depends on where you are taking the voltage reading from and to. On the source side of the terminal there will be a reading of 120 volts to neutral or ground. On the other side of the contact terminal there will be zero volts to the neutral or ground. This is because that wire is in series with the load to neutral. A meter reading across the relay terminals will read 120 volts.

An under voltage relay works by detecting changes in voltage and adjusting output as needed. It can also cut off power if voltage drops too low.

The normally closed contact on a relay is the one that you can see physically touching each other. Remember that all readings are taken in the de energized state, e.g. no voltage applied to the relay's coil. When a relay is energized a Normally Closed (N.C.) contact will become open and vice versa a N.O. contact will become closed.

A relay is a device that uses a lower voltage to switch or control a higher voltage connection or path. The control side uses a coil typically to control a solenoid that opens or closes a contact. In a power substation it might connect or disconnect a source of power to the grid.

A voltage monitor relay is in the circuit for one reason. It monitors the incoming voltage to the equipment that it is protecting usually on three phase control panels.The relay monitors the three incoming line voltages and in some relays the voltage to ground (wye connection). If the circuit the relay is protecting looses one of the voltage legs, the circuit will shut down until the problem is rectified. This usually happens if a fuse blows in one of the three phase voltage legs.It also monitors the level of voltage to the circuit. If the voltage drops due to a malfunction in the utility lines the relay will trip and take the protected circuit off line. The voltages can be set to trip at any under or over voltage usually by set point controls on the front of the voltage monitoring relay.

It is a type of relay used to read the status of Breakers as well as isolators in scada system. As RTU operates at a voltage of 48V and Control panel operates at 110v inoredr to differentiate these potentials it is used

It is the relay that senses the system voltage and sends signal to circuit breaker to cut off if the voltage goes below a set point.

No, they are not the same. A resistor is a current reducer and a relay is essentially a switch (using low voltage to switch high voltage on/off)

PCM means Powertrain Control Module A relay is a low voltage switch

A relay is a kind of electrical switch which interconnects an electric circuit. It works using an electromagnet which makes or breaks a contact when a voltage is applied to the coil. It is activated immediately when voltage is applied. In a relay delay, the electromagnet is not energized instantaneously when a voltage is applied. It is activated after a fixed set of time or programmed time.Various types of delay mechanism are available, some fixed, some with variable time delay. The timing mechanism can be mechanical, motorized or electronic.

The way you check to see if an under voltage relay is wired properly is to disconnect the electrical supply. If the device that is connected to the load side of the relay does not start up or energize when the electrical supply is reconnected, then the relay is connected correctly.

current relay are using for over current low state &amp; high state.but potential relay are related to voltage.

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