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Dont be too critical. CAPS make it easier for those who are sight-impaired. Regards, Phil Corso, PE (Boca Raton, FL)

Just a cautionary comment to advocates of AC to DC operation of a relay: Typically AC designed coils are furnished with a "shading coil" in the magnetic structure. It is used to reduce "hum" vibration. Sometimes this feature will adversely affect the "dropout" voltage of the relay. In the...

Johan: This time I agree... to disagree! The last time we got into a agree/disagree contest was over the definition of the word "almost!" I would prefer to debate you about a more substantive topic. However, for the time being I wish to disagree over the definition, nay, interpretation of the...

Responding to Wajira's Jun 28, 2:40pm, query: The following observation is being made without knowing installation specifics nor hardware parameters> Also I have assumed that "sudden blast" means arcing. One possible cause is contact "chattering" of the loading resistor relay. The relay's coil...

In response to Johan's Jun 8, 11:03 am reply on the subject: What you propose is a misleading oversimplification. The two loads are connected to a three-phase, 400 V, source. Hence, each of the three phase conductors will carry a different current. I'm sure you are not recommending that the two...

Can you provide some informaton regarding the "load(s)?" Regards, Phil Corso, PE (Boca Raton, FL)

Responding to David McConnell's Jun 15, 5:14pm reply on the subject: David makes a good point about DC load current interrupting capability. Thus, it is best to check with the relay manufacture because contact life (number of operations) is based on the time constant (L/R) of the load circuit...

I believe that many respondents to the subject have overlooked the reason for the PID control action function block. Some respondents replies covered the specifics of application. Others presented individual experience to prove, or disapprove expected performance. Both missed the point. The PID...

Replying to David Brown's Jun13, 11:42 am comment: Not necessarily! A PTC (Positive Temperature Coefficient) resistor can be used. They are even commercially available to eliminate centrifugal switch starting of single-phase motors having start-run windings. For those interested look at...

Yes, but not for this small a load. Regards, Phil Corso, PE (Boca Raton, FL)

The following is a general comment regarding the use of flame detectors: Starting with the three most prominent concerns, in my experience, when using (Loss of Flame) Detectors for flame safeguard systems: a) If used in 2 of 2 logic, i.e., both must sense flame loss to cutoff fuel to burner...

Correction to my earlier response: Use the ac rating of the MOV for the ac case! Regards, Phil Corso, PE (Boca Raton, FL)

Responding to Johan Vereecken's query: You haven't stated if the relay coil is ac or dc. The most likely cause of the voltage transient occurs when the relay deenergizes. In rare instances an ac coil's inrush current can be be the cause. Mount a transient suppressor in parallel with the coil...

Responding to Marc Hens' original query on the subject: I have interpreted that the load is 7 kW, single-phase, rated 32 Amps @ 220 Volts. There have been some suggestions regarding supplying the load from 3-phase power source. This, of course, assumes that the 7 kW load is reconfigurable into...

Further to my earlier response to Tom Gianni's query(ies): a) Please note correction. The value, 25, in the penultimate paragraph should read 25 ms. Also, what are DC Bus voltages? b) The use of two fuses (for cost reduction?) should have served as a portend of events that followed. As you...

In response to Tom Gianni's query: Even with a zero-ohm short, the maximum current can not be greater than that which the source can supply. Unless there is some feedback energy from the "drive" the current can't be "amplified" by "switching" devices. Supply fuses must be capable of...

Responding to S. Chimalkar's query dated Wed, Mar 28, 1:31 pm on the use of a 230 Vac fuse in a 24 Vdc circuit: For overloads the fuse will respond to currents in excess of 2 Amperes. However, whether or not it can safely clear short circuits is dependent on the available dc fault-current at...

Responding to C. Thomas Weisen's query dated Tue, Mar 27, 10:21am on the subject of Fuse Applications: One excellent primer (pronounced primmer in the UK) is the National Electric Code (NEC). Produced by the National Fire Protection Association (NFPA), it is known as NFPA-70. Another is the...

This is in response to Anthony Kerstens' Fri, Mar 23, 5:18pm query: Both the R-class and J-class are available as the Dual-Element Time-Delay (TD) type or as the Fast-Acting (FA) type. I believe you will find that the original "J" fuse was the FA type. The replacement "R" is probably the TD...