This is really to 4LORN, but I can’t find him in the drop down:
My electrican has agreed to help me design the feed and wiring layout for my addition…first job will be to splice some 4-0 to extend the feed to a new distribution panel location. Discussing the splice, he mentioned the latest technique involves plastic cylinders full of (silicone?) that are supposed to seal as good or better than splice blocks and heat shrink. I’ve seen these at the big box, but decided against them for a different underground splice after 4LORNS excellent “how to” on heat shrink splices.
Which would you recommend…the new ones or good old splice blocks and heat shrink?
Replies
I appreciate your faith but don't discount the other electricians who post here or the one on site. Most of the posts by others dealing with electrical issues are sound and well thought out. They cover the subjects well enough. I usually differ on only the finest and most esoteric of points. My answers are only more comprehensive because I'm long winded.
Silicone filled splice blocks, these usually are rubber covered and use a hex key to tighten, have a long history with utilities. These have largely replaced split bolts and wrapped insulation. Insulating split bolts or uninsulated splice blocks is labor intensive and a bit of an art form to do well.
Many of these blocks are "direct burial" rated but I have seen a few fail due to soil chemistry or being under water. They are best used in accessible splice boxes below grade or in above ground junction boxes where the water remains below the splices and the blocks can be held in air with only short term exposure to soil and water.
The type of underground splice box best used IMHO is one rated for vehicular traffic and mounted with the lid just proud of flush with the finish grade to prevent it becoming a dry well draining your lawn. The vehicular rated model cost a bit more but save trouble if someone gets wild driving service trucks and are generally tougher. The boxes are relatively unobtrusive and, as long as they are intelligently located away from vital sight lines, shouldn't interfere with the look of the landscaping.
The box makes finding and checking the splices easy. Eliminating the need to hunt and dig. If the splices are installed make sure to give yourself enough slack to allow the splices to be pulled above ground level and still give you some to spare if a splice fails and a conductor or two burn back a bit. Splicing into existing lines where there is little slack it can pay to install two small boxes several feet apart with new conductors between them to give you the slack. You could go with a much larger box but I have found that large boxes are much more expensive that two smaller ones. The slack, properly positioned, also supports the splice blocks vertically so they drain and are above the soil and any standing water in the bottom of the box.
For smaller conductors, where there is a high water table and where the splice will be buried and forgotten I try to avoid splice blocks preferring a more tightly sealed type of splice. This is why I didn't mention them in the previous discussion. Properly used and in the context of a splice box or j-box, where replacement is easy, a well installed splice block should serve quite well for the situation as I understand it.
Don't discount splice blocks entirely if your water table or soil conditions are not favorable. You might be able to mount a junction box above ground, low enough to be hidden by vegetation but high enough to beat any flooding, as an alternative to the underground version.
Sounds to me like your electrician has the situation well in hand.
I like the splice-box idea. There're unobtrusive and always accessible.
Ed