Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Recent content by robbm

  1. robbm

    480V delta source for 480V wye system?

    We have a system that is designed for a 480V wye system, and the customer came back stating that their power source has 1 leg grounded (ie delta). Not having dealt with this in awhile, do I just need to make sure any 3phase devices are rated for running off 480V delta? Regarding the devices on...
  2. robbm

    info on SIL-certified power supplies?

    Our sales group is quoting a project where an engineering firm has listed out that the safety circuit be powered from a SIL-certified 24VDC power supply. I've gone through the few different brands we typically use for our power supplies (AB, Carlo Gavazzi, Sola) and have found the units have...
  3. robbm

    Simulating PLC load w/Loop Powered Device

    This is for wiring a transmitter without a PLC, so that's why I posted it here...
  4. robbm

    Simulating PLC load w/Loop Powered Device

    I have a 4-20mA transmitter that I need to power up just for using the display on the unit, there's no PLC in the application. I thought 250ohms was the minimum resistance i'd have to wire between the 24VDC supply and the transmitter to simulate the load of the PLC, but wanted to confirm if my...
  5. robbm

    will (3) 1pole MCCBs trip before a 3pole MCCB if only 1 leg shorts?

    xnuke, that looks like something that could work, i'll just have to check on sizing, since some of our heaters range from 8A up to 85A, so there's some large ones it wouldn't work for, and most of our systems are 480VAC, not 208-240VAC, but maybe there's expanded options and sizes/voltages...
  6. robbm

    will (3) 1pole MCCBs trip before a 3pole MCCB if only 1 leg shorts?

    I was having a discussion recently and wanted to see if I could get some clarification/opinion on a suggestion I received recently. We have an issue with a 3phase electric heater that is wired in the head and the lack of space has caused the leads to break off and touch the housing sometimes...
  7. robbm

    2 transformers/voltages, both neutrals tied to ground

    True. This project we are using ultrasonic generators that are only made in 230vac models and aren't UL-listed because of the leakage current, and due to that any GFCI used to allow it to be UL labeled trips when we try using it. Any suggestions that would allow us to label it would be welcome...
  8. robbm

    2 transformers/voltages, both neutrals tied to ground

    ok, thank you. we plan on separating/labeling the neutrals to two different connection points, but electrically, they'll both be connected to ground. Not sure of the UL issue either, but this particular panel cannot be UL-labeled anyways, so that won't be an issue.
  9. robbm

    2 transformers/voltages, both neutrals tied to ground

    We have a control panel in which we'll have 2 transformers (460x115 and 460x230). The neutral of our transformers is usually wired to a 'neutral' terminal and also grounded to the backpanel. Is there any issue with both transformer neutrals being grounded to the backpanel, thus both voltages...
  10. robbm

    fuse protection for resistive heater load

    jraef, while the NEC doesn't require the 125%, UL508A 31.6.1 says the load shall have branch protection of at least 125% of the heater load, and not larger than the field wiring ampacity rating. sounds like we are just going to use UL489 breakers from now on. racookpe1978, these units are sold...
  11. robbm

    fuse protection for resistive heater load

    that helps, thanks. our heaters are only 50-250F heaters, so the resistance should likely be less than the 14% in your example, correct?
  12. robbm

    fuse protection for resistive heater load

    dave, thanks. looks like whomever here started the process of using the highspeed fuses was misguided, so we'd probably be best switching to a thermal mag or a dual element. surprised now to think we haven't had more issues with fuse blows at startup more often... thanks again.
  13. robbm

    fuse protection for resistive heater load

    another option my boss asked was if there's any harm in using a 3pole UL489-rated CB in place of fuses. i'm trying to go through curves of certain breakers vs. the highspeed fuses vs. dualelement time delay. any thoughts?
  14. robbm

    fuse protection for resistive heater load

    ok, thanks. that makes sense, since UL508A also states the heater loads must be sized for at least 125% the heater load current (so a 50A is about the lowest to the 37A load as we can go). If it isn't a significant inrush, i wouldn't think a 50A fuse should be blowing from just coldwater being...
  15. robbm

    fuse protection for resistive heater load

    i didn't see a UL requirement either, but we've used the high-speed type since before my time here and i've been trying to find the reasoning beyond just protection of the device. we have had the heaters burn up from being on and running without water, etc, even for a short time, so we...
See more

Part and Inventory Search

Back
Top