Looking at several different types of components (switches, relays, fuse holders, cable, etc.); I wondered what the current ratings were. Most were rated at 230v AC. if the components are used at a low voltage, and with DC instead of AC, what effect would this have on the current rating?
Say I have a fuse holder, and is rated at x amps at y volts, AC. what would the rating be at z volts DC? How can I work this out? For cable, I can look at the thickness, but without actually testing them to destruction, how can I find the current rating of other components?
I have some fuse holders rated at 13A 230V AC, and I have some 15A fuses. Used at say, 12v DC, will the fuse holder melt before or after the fuse?
Any help/advice appreciated.
Say I have a fuse holder, and is rated at x amps at y volts, AC. what would the rating be at z volts DC? How can I work this out? For cable, I can look at the thickness, but without actually testing them to destruction, how can I find the current rating of other components?
I have some fuse holders rated at 13A 230V AC, and I have some 15A fuses. Used at say, 12v DC, will the fuse holder melt before or after the fuse?
Any help/advice appreciated.
for current interruption devices, generally 250VAC devices
are rated at 160VDC, the difference due to the zero voltage /
current crossing nature of AC voltage/current.
For thermal ratings e.g. cables voltage is relatively immaterial,
current counts, AC RMS or DC makes no difference.
Fuse holders again voltage is usually immaterial,
but you obviously cannot use them for 3kV.
sreten.
are rated at 160VDC, the difference due to the zero voltage /
current crossing nature of AC voltage/current.
For thermal ratings e.g. cables voltage is relatively immaterial,
current counts, AC RMS or DC makes no difference.
Fuse holders again voltage is usually immaterial,
but you obviously cannot use them for 3kV.
sreten.
sreten said:for current interruption devices, generally 250VAC devices
are rated at 160VDC, the difference due to the zero voltage /
current crossing nature of AC voltage/current.
For thermal ratings e.g. cables voltage is relatively immaterial,
current counts, AC RMS or DC makes no difference.
Fuse holders again voltage is usually immaterial,
but you obviously cannot use them for 3kV.
So you are saying that the current rating is approximately correct for any (sensible) voltage?
The voltage rating is for the voltage it is guaranted to not Arc-Over (has to do with the spacing between parts).
The current flowing through a part generates heat, so the current rating is the maximum current that the part can handle without getting to hot (above a specified limit, such as to meet a UL/CSA/CE rating). So this means that curent rating is the max for any voltage, doesn't matter except there is a difference between DC and AC current ratings.
Note that switches and relays are spec'd for resistive or inductive loads as these behave differently.
The current flowing through a part generates heat, so the current rating is the maximum current that the part can handle without getting to hot (above a specified limit, such as to meet a UL/CSA/CE rating). So this means that curent rating is the max for any voltage, doesn't matter except there is a difference between DC and AC current ratings.
Note that switches and relays are spec'd for resistive or inductive loads as these behave differently.
It should not matter in the case of that fuseholder.
BUT..........
if it has printed on it 20 Amps AC, I would derate it for DC current.
(some relays will have an AC amps and a DC amps rating on them)
(I looked at two Fuse web sites but it seems that they are reducing the ammount of information they carry thesedays)
Are you going to be running close to 20 Amps?
BUT..........
if it has printed on it 20 Amps AC, I would derate it for DC current.
(some relays will have an AC amps and a DC amps rating on them)
(I looked at two Fuse web sites but it seems that they are reducing the ammount of information they carry thesedays)
Are you going to be running close to 20 Amps?
crown300 said:
what do you think would be a sensible DC rating?
most websites seem to have less and less information on them, unless you pay.
not this one though no, probably 15A maximum. (worst case) the voltage will be between 12v and 40v DC. i wasnt looking at that particular fuse holder, it was just an example.
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