trat1208
Electrical
- Jan 22, 2009
- 15
Hi,
Had a question about contact ratings related to a simple circuit . . .
In a new substation being built I have a SEL-2506 I/O module with 125Vdc inputs for wiring in miscellaneous building alarm contacts (125Vdc battery charger alarm, HVAC alarm, etc). Additionally, an H2 detector is being installed above the battery with an alarm contact that I'd like to wire up, but the manf literature says the alarm contact is rated for 0.5A@28Vdc and 0.5A@125Vac. So my contact does not have a 125Vdc rating and my DI's must be wetted with 125Vdc battery voltage (SEL-2506 does not allow the flexibility of wetting the DI's with AC or DC). The SEL 125Vdc digital input draws 4ma.
My gut tells me that this should be fine - the 125Vac rating indicates that it shouldn't have an issue with the contact arcing over when it's open and the 0.5A@28Vdc tells me that it has some ability to break DC current (well above my 4ma). Also, I kind of suspect that this probably isn't uncommon to do, just judging by the fact that I've seen things like thermostats, door alarms, sump level floats, etc wired to 125Vdc utility substation SCADA I/O in the past and I'm thinking it's hard to find items like those with 125Vdc contact ratings.
Obviously, a way to avoid the whole issue is to wire this alarm to a 120Vac coil interposing relay with 125Vdc contacts to pick up the digital input, at the expense of an added relay and some additional complexity. But worried that'd be making a mountain out of a molehill.
Curious to hear any advice.
Had a question about contact ratings related to a simple circuit . . .
In a new substation being built I have a SEL-2506 I/O module with 125Vdc inputs for wiring in miscellaneous building alarm contacts (125Vdc battery charger alarm, HVAC alarm, etc). Additionally, an H2 detector is being installed above the battery with an alarm contact that I'd like to wire up, but the manf literature says the alarm contact is rated for 0.5A@28Vdc and 0.5A@125Vac. So my contact does not have a 125Vdc rating and my DI's must be wetted with 125Vdc battery voltage (SEL-2506 does not allow the flexibility of wetting the DI's with AC or DC). The SEL 125Vdc digital input draws 4ma.
My gut tells me that this should be fine - the 125Vac rating indicates that it shouldn't have an issue with the contact arcing over when it's open and the 0.5A@28Vdc tells me that it has some ability to break DC current (well above my 4ma). Also, I kind of suspect that this probably isn't uncommon to do, just judging by the fact that I've seen things like thermostats, door alarms, sump level floats, etc wired to 125Vdc utility substation SCADA I/O in the past and I'm thinking it's hard to find items like those with 125Vdc contact ratings.
Obviously, a way to avoid the whole issue is to wire this alarm to a 120Vac coil interposing relay with 125Vdc contacts to pick up the digital input, at the expense of an added relay and some additional complexity. But worried that'd be making a mountain out of a molehill.
Curious to hear any advice.
