Q&A FOR Webinar on Electrical Basics & Boiler Wiring 4-20-16 Q: Is a dual fuel burner flame guard system more complicated than the one you showed us today? A: Not really. If the boiler is equipped for dual fuel burning, it will have a simple selector switch which puts you in either the gas or oil firing mode. The sequence the BMS follows is then the same, only the devices controlled are different. Q: Single phasing of 3 phase motor destroys motor how can this be prevented? A: Single phasing means one of the phases is open causing increased amperage draw as the motor seeks to reach its full rated capacity or horsepower. Protection for the motor in this situation is through the use of three properly sized overload relays, inherent motor protection, and/or three dual element fuses. Good question! Q: Where are your Electrical BM courses offered? A: Our boiler maintenance courses are offered at your facility with a tailored program, at a CB Rep. sponsored regional site or, at our training facility (The CB Boiler House and R&D Center) in Milwaukee, WI. Q: When does pilot drop out? How long after the main burner is lit? A: The pilot should extinguish right after the main flame is proven by the BMS/Scanner. Q: Are you going to consider a class on controls such as building controls Backnet or direct digital controls, ddc? A: We have had a couple of webinars covering controls, but have not concentrated on those subjects specifically. It s an excellent suggestion, and one we will certainly consider for the future. Thank you!! Q: Is this presentation applicable to Fire tube as well as water tube boiler? A: Absolutely! Q: Is the BMS different than CMS - Combustion Monitoring System? If yes, in what manner? A: The answer is yes. The BMS is the supervisor and sequencer for all of the burner functions from proving initial power at our hot and neutral wiring connections to post purge and shutdown of the burner once the load is satisfied. The CMS, also referred to as the CCS or Combustion Control System, is there to provide other energy and safety functions including full metering of fuel and air, cross limiting, oxygen trim, two or three element feed water control, etc. The BMS and CMS/CCS are separate systems, but functionality is totally integrated.
Q: Which system (BMS or CMS) controls Flue Gas Oxygen and Air Emissions? A: The CMS. Q: Are there safety hardwire interlocks around the BMS to avoid failures in the BMS causing high hazard by not closing the safety shut of valves in a gas system? (For example e-stop hard wire to close the SSVs, power failure to the BMS...) A: Yes Q: What dictates if a safety device is manual reset or automatic reset? A: This is controlled by NFPA standards, local codes, customer preference, and Insurance requirements. Q: Is BMS basically a safety system where as CMS is a system that responds to changes to the load? A: Not really. The BMS is totally integrated with the firing rate control also known as the modulating control which is sensing the system pressure or temperature and sending a signal to drive the fuel and air valves open or closed as the system load varies. Q: How many control systems do you typically see your equipment controlled by which are non on board? A: Control systems which are not part of the boiler manufacturer s design and applied to the unit at time of manufacture cannot control the operation of the boiler as it relates to any safety limits and functions. This limits those extraneous controls to (possibly) turning boilers on and off, and monitoring. Q: Can PLC control replace BMS with same functionality? A: Actually, the PLC becomes the electronic platform, and will incorporate the BMS which normally is manufactured by either Honeywell or Fireye. Q: Recently we have purchased a fire tube boiler. Is BMS and CCS fully described in the manuals? A: The manuals you received with the unit should include all the manuals you need with complete detail. If you are lacking anything, please contact your local CB representative who if they can t assist, will call us for help. Your complete satisfaction is our ultimate goal, and thank you for your business! Q: How could damper position affect blower motor amperage? A: As the air damper blade or air metering system begins closing to reduce the amount of combustion air, the static pressure increases; increasing the amperage draw on the motor. This can be largely mitigated through the use of a variable speed drive on the motor. Q: From an experience perspective- As the ability to troubleshoot burner wiring issues, what do you see as the min amount of time (years) before a technician becomes a true expert in burner wiring?
A: This is totally dependent on the individual and their innate ability to grasp the theory of electricity and wiring logic. Some people with this ability can attend one class on how that particular equipment is designed and wired, and be safe and productive in a matter of a few weeks (Rare, but it happens). Others of average or below aptitude will struggle a bit, and besides a basic wiring course on electrical theory, and related wiring logic, will need field mentoring and tutoring before they are reliable with the equipment and its electrical issues. I d say this could mean several months of training (class & field) before they are productive, reliable and safe in the field alone. The other variable is system complexity involving both PLC based logic controls working in concert with electromechanical devices. This gets tricky even for the most blest in the area. Here it boils down to training and hands on experience, the timing of which varies based on exposure. Q: What is difference between 240VAC and 230VAC A: Very small difference in EMF (Electromotive Force) which has little impact on the motor its driving. Q: What is the maximum length of wire for a 4-20ma transmitter, using a 3 conductor 22 awg cable? Example header steam pressure transmitter to master panel. A: There are two factors that affect the maximum length. This is the resistance of the shielded instrument cable and the 24VDC power source that is driving the loop. The Belden 3105A, #22 AWG shield cable used by Cleaver- Brooks has a resistance of 14.7 ohms per 1000 feet. Kirchhoff`s second law states the sum of all voltages in a circuit is 0. The master panel PLC analog input module has 250 ohms of resistance, which equates to 5VDC @ 20mA (0.02 amps). See example below of analog loop with voltage drops and resistance (ohms) at each major component in the loop. As shown below, the cable length is 3,700 meters which is 12,139 feet. This is an extreme example, but as you can see a 4-20mA signal can be run in a typical boiler room without any concern for exceeding the maximum cable length. It is recommended to use an instrument cable larger than #22 AWG for significant length runs and #18 AWG would be a sized cable to use. When running CAT 5 Ethernet cable, the maximum cable run is 300 feet and if this distance is to be exceeded, then fiber optic cable is required.
How does AC current flow to where it needs to go when its traveling in both direction? A: Even though the current flows in both directions at a frequency of 60 cycles per second, as the resistance increases during current flow, you have a potential difference occurring which moves the power along to the place with the least electrons. Isn t voltage really the power in the circuit? A: No, actually voltage is the electromotive force we best describe as pressure. The power is really measured in Watts which is determined by multiplying voltage times amperage which is determined by overcoming one ohm of resistance with a single volt. In our facility we use the terms ground and neutral as meaning the same. Problem? A: Yes, from a safety perspective it is Technically neutral is really a common wire allowing for the flow of current. Ground, is really a safety wire which normally does not have current flow unless there is a short or a floating neutral which might allow current to flow to areas on the equipment where severe shocking could occur. That is why ground is exactly that, a pathway for the current to be safely discharged.
In your example with AC power you re going from 10 amps at 4800 volts and wind up at 100 amps at 480 volt. How did you get to 100 amps? A: We re back to Ohm s law which states you calculate amperage by dividing voltage by the resistance. In the case I showed you with 480 volts coming into the facility the resistance was about 5 Ohms. 480/5 =96 Amps. Why can t DC power be transformed? A: It s really kind of complicated, but it gets back to the characteristics of AC power including a varying voltage and current going from let s say zero to 120 and back again 60 times a second. This is a time delay which sets up a magnetic flux which can tie into the transformer producing a higher or lower EMF on its secondary side. This is not possible with DC voltage because of its unidirectional flow characteristics. We have electric actuators on our boiler controlling the fuel and air. Are these AC or DC powered? A: It depends. If you have a system which is primarily electro-mechanical controlled they are most likely AC powered. If on the other hand you have a PLC based platform, then the AC power is most likely converted to DC to power the actuators you refer to. # # #