Book 5 of the series, "safety sense," goes up to 4
The last one we calculated the site with the electric dishes -- pjs, sjs, ijs. But when we're done with "how much power," we're gonna have to send it to the facilityBreakerIsolated switchesLeak protectionThree types of components to catch。
All the first-line brothers have seen the scene: the locks in the trunk are broken, the switch in the switch is compromised, the labels are sealed, but every time they ask, "is this switch supposed to jump," there's no answer。
It's not that it's hard, it's that sort of thing that's right, and it's what many people do。
This is where we talk about three kinds of components that can be directly targeted at the type. And a quick check card with a "play ijs one stop" to be used on the way to work。
First, we'll separate the three elements from the duties
A lot of people call these three things switches. They do three different things:
Breakers — overload, short-circuit protection
In normal circumstances, power is delivered and the currents are cut; automatic jump is broken when overload (continuous overflow) or short circuits (urgent large current) are detected. It's "the first reaction in an accident," not "the general slash." in the power distribution system, circuit breakers are in two stages:
(b) micro-wire breakers (mcb) — switches, distributions, lighting, small power outlets, end-of-pipe protection of small appliances
Plastic crust breaker (mccb) - the main distribution box, main protection, adequate break-up capability。
Separators — electricity-free boundary
It does not function as a "power action" but rather as a clear and visible cut-off point that allows people to be separated from the electricity when they are being repaired。
Isolation switch rules:
(a) cannot be combined with loads - it can only be operated without electricity or small currents (e. G., transformer empty)
It must be installed on the "power side" of the circuit breaker and the leaked power source, with the total power source cut before the equipment is cut
There must be a visible cut-off point, not to hide in a locker without being seen。
The leaking shield, the leaking thing, depends on it
It specializes in "breeding," which is the undesirable circuit of wire-to-ground, outer-hull electrocution. The principles are in, out and should be zero, otherwise there is a leak。
The site is subject to two levels of leakage:
(b) the main box leaks - to keep "the body of the whole line" to prevent fires and physical electrocution
The switchbox is leaking - the last meter is safe and the person who operates the device can get out of it first
The distribution box is in principle free of leakage and avoids the full stop of the escape belt。
I don't know
Select the first step -- take out the ijs
In book 4, we calculated the main box of ijs≈57a to calculate the current. That's what we're gonna do. All three components are selected from the same main line: rated currents in ≥ ijs, then "use" plus layer conditions。
Four elements of the component selection (any component is over four steps)
Dimensions
What's the question
Common overturns
Rating currents in
In ≥ ijs (1. 25 times normal)
It's always the tipping point
Polar numbers and connections
Single/triple/n/pe
N, error, pe, lack of space, confusion
Discrepancies icn
What's the short-circuit current at that location
Instead of a plastic shell with a normal nuance, it's not enough to blow a container
Deductive properties
B/c/d curve (time-in-time multiples 3-5/5-10/10-20 in)
End-to-end power motors start high, c. Misuse b and jump
One sentence — choosing what doesn't matter, it's important to go up ijs, not to fractal and decorate curves。
I don't know
Iii. Selection of breakers
1. Selecting the polar numbers and segments by location
Location
Breaker recommended
Key points
Total distribution box
Tripolar + break zero (n polar), plastic shell mscb
In ≥1. 25 ijs; to be accompanied by n extreme protection; break-up capability
Distribution of electric boxes
Tripolar mini-mcb + separatist switches
Usually no bail is installed to avoid crossing the escape; divides set aside for 1-2 roads
Turn it off
Tripolar or unipolar mini-mcb
Single device "a switch leak"; leak prefix; single + leak combination for lighting
2. Select in by ijs
Ijs=57a → in choose 80a or 100a
Don't just pick the 63a line, it's easy to jump when the power starts。
The tower hangs the single track 40a → selects 50a or 63a。
(b) a frequently activated motor class, using the d curve (10-20 in instantaneous), not using the c curve, or jump as soon as it is activated
Lighting, plugin class c curve (5-10 in)
Resistible loads (e. G. Water heaters, electro-heat wind cannons) use the b curve。
Icn cannot be saved
The transformer short-circuit current at the site is usually at 6ka-10ka, individually to 10ka+. The end-end icn selects 4. 5 ka to be assured; the main box has to be checked for ≥10ka, otherwise the circuit breaker will "scramble" or even blow up the cabinet in case of a real short-circuit accident. This is the most common hazard in the first line, and many cabinets are barely closed on the basis of their ability to break。
I don't know
Iv. How do you choose the quarantine switch
The quarantine switch isn't a little switch. It's got rules:
1. There must be sufficient heat and stability
The quarantine switch is capable of withstand the impact of installed short-circuit currents, with icw (short-lived electrical currents) on the bottom sign. Select the icw ≥25ka/1s type on the main trunk, which is the bottom line。
2. Disconnection points must be clearly visible
It can't be "button" or "thrower" invisible. The first line of "separation switch looks like a breaker" problem, mostly here。
3. Requires n to go first
N the polar tentacles should be combined before the line, avoiding neutral point drift leading to the burning of low pressure equipment. This structure is specially available in the isolation switch, so don't try to make it easy。
4. Positions relative to breakers, leakages
Power side oscillation switch → leakage breaker → load or power side oscillation switch → breaker leaked load (recommended, usual order at end of single-/ third-phase)
In either order, the quarantine switch must be as close as possible to the power source, and retrofitting it is tantamount to "pull the electricity."。
I don't know
V. How do you choose to cheat
1. Two levels, three sets of parameters
Organisation
Rating remaining action currents iΔn
Break time t
Remarks
Total distribution box
100 – 300 ma
≤0. 2 s (optional with delay)
Select type; to fit with lower level
Turn it off
30 ma
≤ 0. 1 s
The last meters that the operator is in direct contact with
Switching tanks at wet sites
15 ma
≤ 0. 1 s
Rainy season/basement/water harvesting
IΔn x t ≤ 30 ma. S (this formula appears repeatedly, remember)。
2. Selective vs normal (failure also "slotting")
Normal type of leakage (ac or a) - low price, faster the leaking power flow
Selective leakages -- both top and bottom loads can distinguish between "who should jump first" and avoid a massive power outage。
The upper and lower tiers of a complex site have to choose a model with an s (selective) sign, not the usual -- that's the multi-level protection "symmetry."。
3. We're gonna try and jump
The current national standard gb/t 13955-207, installation and operation of residual flow protection devices, emphasized the need to jump once a month by the test button after the leak has been installed and to replace the invalid on the spot. The worst state on the line is when it's leaked and it doesn't jump。
4. Leak a box at one gate (repeated as it is impossible for someone to do)
One device, one switch, one leak, one leak, one lock, one leak, one box. This is one of the elements of title viii, but as the bottom line of this section, you should crucify this sentence。
I don't know
Vi. Recommending the flow of "put on ijs one point"
It's a little bit of a process, so the electrician can take the drawings:
1 take ijs (4th quoted) 2 select main switch: mccb, in≥1. 25 ijs, icn≥10ka3 leak: iΔn 100 – 300ma, with s select 4 separatist switch: icw≥25ka/1s, visible breakpoint, n-plus 5 distribution box: mcb + isolation switch: isolation switch + mmb + leakback (iΔ30ma/ 0. 1s, wet ≤15ma) 7 single turnback: d curve powering motors, c curved plugs, b curved powering hot
I don't know
Vii. Quick-check cards for three types of element for electrical transmission
The screenshots are kept in the class/project cluster to facilitate on-site comparison by duty electricians。
Breaker = normal combination; overload, short-circuit automatic jump。
The main case is made of plastic case mccb; the small case/switch box is used by mcb。
In ≥ 1. 25 ijs。
Electrical curves with d, plugs with c, electric heat with b。
Isolated switch = overhaul of the clear cut point of the "isolated human power"。
Must be the most power-dependent; n, very first-in-time; icw, 25ka/1s; visible breakpoint。
The leak shield = the person specializing in the leak。
General boxes: 100-300 ma, 0. 2s, selective。
Switches: 30ma, 0. 1s; humid sites 15ma。
Ign. T 30ma. S。
Try dancing once a month。
Thread a sentence: power → separating switch → leaking → breaker → device (n and pe are continuously open, pe is severely disabled)
Last issue we talked about the ijs algorithm, and this issue we put the element from the concept to the parameters. The next one, along this main line, how we put the line that we're going to figure out on the ground — empty, penetrating, buried straight, cable bridge frames, choices and taboos about every way to fit it。
What kind of "parameters" do you get stuck most often? Discretion or leakage? The message tells me that i'm going to take it down on the high frequency。
This is title 5 of the " engineering safety man depth " , which implements the jgj/t46-2024 technical standards for temporary electricity security at construction and municipal works sites, with a practical selection proposal for review in conjunction with the product description and the project-specific programme。
Source jgj/t46-2024 technical standards for temporary electricity safety at construction and municipal works sites. Gb/t 13955-2017 installation and operation of residual power flow protection devices). Gb/t 14048. 3-2025, low-pressure switches and control equipment part 3: switches, separators, separators and combination devices. Gb 50054-2011 design code for low-voltage distribution。
