INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS
If you are looking for more details, kindly visit Fuse Cutout Switch.
FIRST NAME
*
LAST NAME
*
*
MESSAGE
*
ADDITIONAL DETAILS
Thanks. We have received your request and will respond promptly.
Log In
Are you an
Engineering professional?
Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving . By joining you are opting in to receive .
Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Eng-Tips Posting Policies
fused cutout as a service disconnect
2
thread238- Forum Search FAQs Links MVPsForum
Search
FAQs
Links
MVPs
(Electrical)
(OP)
19 Aug 09 09:36I have a question on what qualifies as a service disconnect. I have a 25kv service feeding a KVA transformer. The utility company is providing the primary underground, but the transformer (customer owned) has top bushings and I have to transition up a pole and feed it from overhead. The NEC says that a disconnect is required and that no more that 6 six throws of the hand to turn off all power. Would three (one per phase) pole mount fused cutouts qualify as this means of disconnect? This seems to be the norm for utilities. Any advice is appreciated.
Thanks,
Jim
(Electrical)
19 Aug 09 09:42Are you sure the TX is kVA? That's rather large for fuse protection. Normal fuse protection is up to kVA Tx.
(Electrical)
(OP)
19 Aug 09 10:03Yes, it is a kva xfmr. If not fuses, what do you recommend? This is a solution that S&C recommended.
Thanks,
Jim
(Electrical)
19 Aug 09 10:32I don't see how this could satisfy NEC service disconnect requirement. Service disconnect must be readily accessible. And it has to be a load-break device.
You will need a metal-enclosed fused switch or maybe a pad-mounted switch operable from the ground (without a hotstick).
For a 15 MVA transformer, you really need a primary circuit breaker or circuit switcher.
(Electrical)
19 Aug 09 10:36Fuses are certainly possible at 15MVA, but why? Obviously S&C would recommend fuses for this application since they are a fuse manufacturer. I wouldn't use fuses though. I'd put in a circuit switcher with a air break disconnect switch.
Fuses mean that all you have is phase overcurrent protection, and high side fuses do not do a good job of protecting against low side faults, particularly against low side ground faults behind a delta-wye transformer. A circuit switcher would also mean that you have something to trip for faults between the transformer and the secondary gear. This will help tremendously with arc flash mitigation.
(Civil/Environmental)
19 Aug 09 12:26I doubt that the transformer disconnect would fall under NEC, but if it does, the NEC requires that it be labeled "Suitable for use as Service Disconnect".
Steve
Contact us to discuss your requirements of what is the purpose of a washer. Our experienced sales team can help you identify the options that best suit your needs.
(Electrical)
19 Aug 09 19:02Six disconnect rule at 25kV, 15MVA transformer?Start with your local inspector see what he/she says and post it here. You can also send an to NFPA (you need to become a member) and ask for informal interpretation.
Rafiq Bulsara
http://www.srengineersct.com
(Electrical)
19 Aug 09 21:47NEC 230.205: "Each service disconnect shall simultaneously disconnect all ungrounded service conductors that it controls and shall have fault closing rating that is not less than the maximum short circuit current available at its supply terminals."
Alan
----
"It's always fun to do the impossible." - Walt Disney
(Electrical)
20 Aug 09 07:53The logic behind the rule is that a fireman can find and shut down power to a building. Few ( none I hope ) inspectors would buy into a fused cutout as a disconnect. A secondary a circuit breaker with a remote switch is the way I would go. Depending on locaion of the transformer I would use a high sied circuit switcher.
When they show up to put your fire out they want a dead building. If they have to aim the water at just the secndary side of the transformer they will just watch.
(Electrical)
20 Aug 09 21:24An anecdote to go with BJC's response: There was a fire reported in a telecom switching center. The fire dept arrived and asked if anyone was in the building. They were told no, and thus responded that they would not be going in until the smoke cleared. And those places have pre-arranged power procedures sequences for just such situations.You need a readily accessible and properly rated service disconnect that doesn't require qualified personnel to operate.
Alan
----
"It's always fun to do the impossible." - Walt Disney
(Electrical)
21 Aug 09 16:43Where is the metering point? Typically the utility will provide fault protection up to that point.Does the transformer have internal fusing, or protection?Absolutely check with your local inspector to see if he will even take on the responsibility of looking at it.As a utility, we have customers that are primary metered, but we still provide the protection and disconnecting means for each transformer. Although the largest transformer on our system is a kVA at 12,470. We use fused cut outs for our disconnects. Few companies and fire departments have personnel qualified to us a hot stick to open fused cutouts, particularly at 25 kV. They are manually operated, so they cost less than a relay controlled circuit switcher or breaker. Our 15kV, 600 amp switches cost us around $2,000.00.Try looking at gang operated switches that are load-break and load-make rated. They do not provide fault protection, but a single operation will open all three phases simultaniously so you don't have to deal with single-phasing on your large motor loads.
Happiness is a way of travel, not a destination.
(Electrical)
21 Aug 09 16:51THis is why you should proof-read your posts before submitting them."They are manually operated, so they cost less than a relay controlled circuit switcher or breaker. Our 15kV, 600 amp switches cost us around $2,000.00."This refers to the gang operated switches, not the fused cutouts.It should have read like this:Try looking at gang operated switches that are load-break and load-make rated. They do not provide fault protection, but a single operation will open all three phases simultaniously so you don't have to deal with single-phasing on your large motor loads.They are manually operated, so they cost less than a relay controlled circuit switcher or breaker. Our 15kV, 600 amp switches cost us around $2,000.00.
Happiness is a way of travel, not a destination.
Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.
Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.
Click Here to join Eng-Tips and talk with other members! Already a Member? Login
A fuse box plays a crucially important role in all household electrical systems, yet most people don't know much about it.
It may come as a surprise ' perhaps the correct word is shock ' to learn that many householders don't know much about the central pillar of their home's electrical system. Your fuse box, which includes your switchboard, is the hub of your electrical system. It pumps power to all of your lights, switches, fans and other appliances.
It's important to note that any electrical work, particularly an upgrade, should be carried out by a fully qualified and licensed electrician. Given how integral your fuse box is to your home's safety and the way it functions, it might be time to look at four important things you need to know about your fuse box.
Almost everything electrical in a household goes through the switchboard. The switchboard divides electrical power into 240-volt circuits and distributes them to household electrical appliances.
The fuse box is also an electrical distribution board, like the switchboard. The difference is that while the switchboard distributes electrical power around the house, the fuse box protects circuits from overloading.
That's why fuse boxes are sometimes referred to as 'circuit breakers'. It's vital that fuse boxes are kept up to date and in good working order so that they can do their job of protecting your electrical system.
While on the subject, your meter is something different again. It connects your property to the mains power lines in the street and records how much electricity you're using from the grid. This is how your power bills are calculated.
There are three main components that make up a fuse box. They are:
If you're in a home which is older than 25 years, you'll probably need to have your fuse box upgraded. An older fuse box will have experienced a lot of use, so it can potentially become an electrical fire hazard.
An upgraded fuse box will include safety switches known as residual current devices (RCDs). These devices will immediately cut off electrical supply when a fault is detected.
Circuit breakers protect your outlets and appliances from overload, while RCDs protect people from shock and electrocution. Essentially, RCDs are very sensitive to changes in the current and do save lives.
Some of the signs that you need to upgrade your fuse box are:
Old-fashioned ceramic fuses, also known as SERF (semi-enclosed rewirable fuses), should always be replaced. These fuses often short circuit and are a potential electrical hazard.
Every scenario is different so it's difficult to know exactly how long a fuse box upgrade will take. It depends on the size of the home, the age of the current fuse box and the age of the home's wiring.
For a standard upgrade to a fuse box that is 10 to 20 years old, the job can take four hours or less. In a house that is more than 25 years old, the job might include cabling and rewiring and can take up to eight hours or even longer in older homes.
In homes that are more than 40 years old that have never been upgraded, you will definitely need to get the entire home rewired. Some of these homes still use aluminium wiring, which is regarded as a fire hazard. Copper wiring is considered the safest wiring for homes.
The scope of the job and how long it takes will also determine the cost, but expect to pay $500-$ to replace an old fuse box with a modern one. If your entire home needs rewiring, the cost is likely to be in the $-$ range.
Your fuse box is the electrical power hub of your home. Considering its importance, it might be time to get to know more about it. If you're unsure about the condition and age of your fuse box, get a qualified electrician in for some advice.
Want more information on insulating fitting? Feel free to contact us.